2039 Mile Tow with GMC 3.0 SLT

Sierra 3.0 · June 30, 2020

I just got back from vacation and thought I would let anyone who wants to know what it was like to tow with my 2020 GMC SLT 3.0L diesel. I will include my towing fuel mileage for the trip. I purchased my truck on April 15th of this year. I had an initial build quality issue with it as it was leaking oil when I brought it home. Turns out there was an improperly installed gasket and seal leading from the oil pump to the engine causing the leak. The engine leaked 2 out of the 7 quarts of oil before the problem was found. The dealership fixed the issue and I have been trouble free since.

The truck has 6700 miles as of today. Overall I'm very happy with the power/smoothness of the 3.0 and 10 speed transmission. In everyday driving it's a really nice combo. I know this engine is an unknown in many ways but I wanted better fuel economy and after an abundance of research I took the gamble on the GMC. I really like the look of the truck and I have wanted a 1/2 ton GMC for some time. I'm coming from a 2007 new style Chevy 2500 6.6 Duramax. My average MPG for the 166,****** miles I drove it was right at 14. I kept it stock and used it for occasional towing but mostly commuting. I had very little issues with the truck other than rust that developed over the rear wheel wells.

Last week my family and I took a trip from Missouri to Lake Superior and Lake Michigan on the US side. We left on June 20th and got back on the 28th. We used RV Share to rent a travel trailer in Iowa on our trip to the lakes. The trailer was a 32' Keystone Bullet 277BHS, GVWR 7600lbs. I did not weigh the truck and trailer but I'm sure the trailer was at least 8500 lbs with our gear etc.

I did use a weight distribution hitch that was provided by the owner. It was set up for his Ford F-150 and not for my GMC. I'm sure I could have adjusted it to better control my rig but it worked OK. The only issue I had towing was bounciness on rough roads. If I were to own a travel trailer I would add air bags to the rear of my truck and make sure the weight distribution hitch was completely dialed in.

The truck did a great job hauling my family of 4 and the trailer. I had plenty of power and I did not feel like I needed more engine at anytime during the trip.

The overall comfort in the front seats was fine for long periods of time but the rear seats are too hard and too straight up and down to be comfortable for a long trip. My wife suggested GM could add a slide to the seat bottom so the seat bottom would slide a short way towards the front seats creating a reclining affect. Everything else in the truck worked well.

The trucks GPS was slightly below par compared to google maps but it did get us from destination to destination and was OK while navigating. Using my voice to search for addresses etc did not work well. The voice calling also does not work well when trying to get a contact to pull up from my phones contact list. GM needs to fix this.

I hand calculated my mileage at every fuel up using my trip meter and the gallons needed to fill the tank. I allowed the pump to run until it stopped then waited 20-30 seconds and ran it again until it stopped. I have attached a pic of the spreadsheet along with the trucks computer read out.

In all I averaged 11.73 MPG over the entire 2039.2 miles of towing the trailer. The trucks computer average was 11.31 MPG.

I hope this helps anyone who is curious about this truck and engine combo for towing.

redwngr · June 30, 2020

Thanks for the report.

Interesting that for every fill the actual mpg was better than the dic mileage.

Sierra 3.0 · June 30, 2020

That's been very consistent with regular driving as well. The hand calculation is always better than the computer.

BurnsMax · June 30, 2020

Thanks for the write up! How was your DEF consumption? Mine goes in tomorrow for an oil leak and a DEF recall

Sierra 3.0 · July 1, 2020

4 hours ago, BurnsMax said:

Thanks for the write up! How was your DEF consumption? Mine goes in tomorrow for an oil leak and a DEF recall

I filled up before I left. I used about 15 gallons during the trip. Just FYI...I hate DEF. Its not too bad if you fill up at a pump but if you use the jugs it overflows and leaves nasty white crystal mess all over your truck side. It also makes your hands all sticky.

BurnsMax · July 1, 2020

Yeah that's what I heard about the DEF. I haven't I had to fill it up yet. I have about 3400 miles on the clock and about half a tank of DEF left.

f8l vnm · July 1, 2020

Great write up! thank you

Phatty · July 1, 2020

Great write up! This is so similar to my set up. 32 foot 7k lb trailer that we will be setting out in on Friday for a 1000-1500 mile roadtrip. My previous tow vehicle was 2006 LBZ duramax. I did at the airbags to my 3.0 and set up my distribution hitch. It improved trailer ride dramatically from my first camper run. I think I will hit the scale on this trip just to see where I am at.

Did you measure sag at the hitch or wheel well at all? Have you done this trip with your old Dmax to compare against?

Sierra 3.0 · July 1, 2020

No, I did not measure the drop but I could see it. The steering felt fine and not loose. When I picked it up I just used the same setting he had for his F-150.

I did tow a camper with my 07 Duramax. We took a trip to Texas and went across the entire state and along the Gulf Coast. I seem to remember getting about 10 or 11 MPG for that trip but it was a lighter trailer than the one I towed last week and the computer usually overestimated my mileage instead of underestimating it.

I hope you guys have a great vacation and I know you will enjoy the pulling experience!!

Phatty · July 18, 2020

Well I wanted to report back on my trip. Did 1500 miles with 2 different trailers.

1st trailer is my personal one. 32 foot imagine and we were fully loaded with 2 kids, dog, and toys galore for the week. I’m sure it was over 9k.
we averaged 11.2 mpg at speeds of 75-80 for that 7 hour portion.

We parked the camper and I then drove 4.5 hours to get my sister and her family and her camper and bring them up. Going to get them I averaged 31 mpg at 75mph. This was a 28 foot jayco around 4500 fully loaded.
I got 11.8 pulling that trailer into a 30moh headwind at speeds around 60-65. I didn’t pull that trailer home as her husband came up later with their truck. These was white knuckle drive as I didn’t have distribution hitch and was getting pushed around.

going home with my trailer we got 10.7 mpg with 20 mph headwind and 75mph speed

I didn’t see a lot of 10th gear and spent more time in 7-9. I did get fairly hot on one long 6% grade where I held at 75mph and saw coolant temps to 228 and tranny to 215. 90 degrees outside. Egt were pegged at 1260 for couple miles. But she came right back down. The oil temps on my obd- torque pro never read correctly. Wanted to push the truck and she responded nicely. I’ll slow down to 65 on that pass next time.

were downsizing our trailer soon as warranty expires and in very pleased with how this truck pulls. I include photos of hitch height(21”) hitch sag (17.75”) hitch with distribution bar (19.25”) and with airbags filled (20.25”).

i went through 7.5 gallons of def (full at start and full at end) which seemed like a lot. But we were high altitudes and going over MTn passes and running high speeds towing.

Ojustracing · July 19, 2020

21 hours ago, Phatty said:

Well I wanted to report back on my trip. Did 1500 miles with 2 different trailers.

1st trailer is my personal one. 32 foot imagine and we were fully loaded with 2 kids, dog, and toys galore for the week. I’m sure it was over 9k.
we averaged 11.2 mpg at speeds of 75-80 for that 7 hour portion.

We parked the camper and I then drove 4.5 hours to get my sister and her family and her camper and bring them up. Going to get them I averaged 31 mpg at 75mph. This was a 28 foot jayco around 4500 fully loaded.
I got 11.8 pulling that trailer into a 30moh headwind at speeds around 60-65. I didn’t pull that trailer home as her husband came up later with their truck. These was white knuckle drive as I didn’t have distribution hitch and was getting pushed around.

going home with my trailer we got 10.7 mpg with 20 mph headwind and 75mph speed

I didn’t see a lot of 10th gear and spent more time in 7-9. I did get fairly hot on one long 6% grade where I held at 75mph and saw coolant temps to 228 and tranny to 215. 90 degrees outside. Egt were pegged at 1260 for couple miles. But she came right back down. The oil temps on my obd- torque pro never read correctly. Wanted to push the truck and she responded nicely. I’ll slow down to 65 on that pass next time.

were downsizing our trailer soon as warranty expires and in very pleased with how this truck pulls. I include photos of hitch height(21”) hitch sag (17.75”) hitch with distribution bar (19.25”) and with airbags filled (20.25”).

i went through 7.5 gallons of def (full at start and full at end) which seemed like a lot. But we were high altitudes and going over MTn passes and running high speeds towing.

What did you find wrong with the oil temps? Extremely high? i also have the Toque pro app and one of the pids puts oil temps just cruising were 280+ very quickly. Guess the GM pid reads incorrectly , reading way high and you have to use the generic pid. The generic pid to me correlates to what I feel oil temp should be(10f-20f over coolant temp). But it does look like the active cooling system is used in two ways. One to warm the oil up to aprox 226f-236f. The other aspect to cool off the oil temps above 236f which this truck will do even unloaded.. Its really neat to watch when you are monitoring both pids together. Think this is why many have stated some bigger temp swings, especially once the oil temp reaches just over 200f and the truck is trying to increase the oil temp.. I've seen coolant temps as high as 226f when the truck is trying to increase the oil temps and coolant temps as low as 185f when its trying to bring down the oil temps down from 250f-266f. Interesting technology, different operation from what were accustomed to and would love to talk to a GM engineer about it.

Phatty · July 20, 2020

On 7/18/2020 at 11:10 PM, Ojustracing said:

What did you find wrong with the oil temps? Extremely high? i also have the Toque pro app and one of the pids puts oil temps just cruising were 280+ very quickly. Guess the GM pid reads incorrectly , reading way high and you have to use the generic pid. The generic pid to me correlates to what I feel oil temp should be(10f-20f over coolant temp). But it does look like the active cooling system is used in two ways. One to warm the oil up to aprox 226f-236f. The other aspect to cool off the oil temps above 236f which this truck will do even unloaded.. Its really neat to watch when you are monitoring both pids together. Think this is why many have stated some bigger temp swings, especially once the oil temp reaches just over 200f and the truck is trying to increase the oil temp.. I've seen coolant temps as high as 226f when the truck is trying to increase the oil temps and coolant temps as low as 185f when its trying to bring down the oil temps down from 250f-266f. Interesting technology, different operation from what were accustomed to and would love to talk to a GM engineer about it.

Yes oil temps were like 255-295 constantly. Ill have to add the generic pid.

k_j · September 11, 2020

On 6/30/2020 at 3:12 PM, Sierra 3.0 said:

I just got back from vacation and thought I would let anyone who wants to know what it was like to tow with my 2020 GMC SLT 3.0L diesel. I will include my towing fuel mileage for the trip. I purchased my truck on April 15th of this year. I had an initial build quality issue with it as it was leaking oil when I brought it home. Turns out there was an improperly installed gasket and seal leading from the oil pump to the engine causing the leak. The engine leaked 2 out of the 7 quarts of oil before the problem was found. The dealership fixed the issue and I have been trouble free since.

The truck has 6700 miles as of today. Overall I'm very happy with the power/smoothness of the 3.0 and 10 speed transmission. In everyday driving it's a really nice combo. I know this engine is an unknown in many ways but I wanted better fuel economy and after an abundance of research I took the gamble on the GMC. I really like the look of the truck and I have wanted a 1/2 ton GMC for some time. I'm coming from a 2007 new style Chevy 2500 6.6 Duramax. My average MPG for the 166,****** miles I drove it was right at 14. I kept it stock and used it for occasional towing but mostly commuting. I had very little issues with the truck other than rust that developed over the rear wheel wells.

Last week my family and I took a trip from Missouri to Lake Superior and Lake Michigan on the US side. We left on June 20th and got back on the 28th. We used RV Share to rent a travel trailer in Iowa on our trip to the lakes. The trailer was a 32' Keystone Bullet 277BHS,  GVWR 7600lbs.   I did not weigh the truck and trailer but I'm sure the trailer was at least 8500 lbs with our gear etc.

I did use a weight distribution hitch that was provided by the owner. It was set up for his Ford F-150 and not for my GMC. I'm sure I could have adjusted it to better control my rig but it worked OK. The only issue I had towing was bounciness on rough roads. If I were to own a travel trailer I would add air bags to the rear of my truck and make sure the weight distribution hitch was completely dialed in.

The truck did a great job hauling my family of 4 and the trailer. I had plenty of power and I did not feel like I needed more engine at anytime during the trip.

The overall comfort in the front seats was fine for long periods of time but the rear seats are too hard and too straight up and down to be comfortable for a long trip. My wife suggested GM could add a slide to the seat bottom so the seat bottom would slide a short way towards the front seats creating a reclining affect. Everything else in the truck worked well.

The trucks GPS was slightly below par compared to google maps but it did get us from destination to destination and was OK while navigating. Using my voice to search for addresses etc did not work well. The voice calling also does not work well when trying to get a contact to pull up from my phones contact list. GM needs to fix this.

I hand calculated my mileage at every fuel up using my trip meter and the gallons needed to fill the tank. I allowed the pump to run until it stopped then waited 20-30 seconds and ran it again until it stopped. I have attached a pic of the spreadsheet along with the trucks computer read out.

In all I averaged 11.73 MPG over the entire 2039.2 miles of towing the trailer. The trucks computer average was 11.31 MPG.

I hope this helps anyone who is curious about this truck and engine combo for towing.