6.6L gasser MPG with new 10 speed Allison tranmission?

campah · September 25, 2023

Hey All,

This is my first post and I'm glad I found this forum. I'm considering a new '24 GM Sierra gasser with the 10 speed Allison transmission. I looked through quite a few pages and couldn't find a thread pertaining to MPG on the new 6.6L with this tranmission configuration. I'm looking to use the truck for a hauling a truck camper and I haven't owned an HD struck before so please pardon my ignorance.

What MPG have you been getting on the freeway and also around town? If you have a truck camper, what have you been getting unladen and laden?

If you came from a previous 6.6l gasser with less gears, how has this been doing in comparison? Was it worth it for the upgrade (as I'm also considering a used truck).

Thanks All,

Matt

the8rotor · September 25, 2023

Gas mileage is the same between 6L90 and 10speed, I've had both. I get anywhere between 11-13.5mpgs city and 18/19mpgs highway ripping around the toll roads in Texas.

Towing my 10-12k camper, I get 5-11mpgs depending on winds on the highway. My camper is very tall.

Another JR · September 25, 2023

I think the OP is talking about a slide-in truck camper. I have a Four Wheel Campers pop up truck camper and I get about 15-15.5 mpg with the camper on and around 17.5 with it off when driving 65-70. It only weighs 1800 lbs. Of course, a tall, heavy non-pop-up camper will be a whole different story.

campah · September 25, 2023

Yes, I am planning on hauling a solid walled, slide-in truck camper using a 3500. I'm coming from a Tundra that gets 13-19 MPG. Those are very reasonable numbers when comparing your HD trucks to my Tundra.

Anyone seeing better numbers if they put on a tonneau type cover?

Another JR · September 25, 2023

25 minutes ago, campah said:

Yes, I am planning on hauling a solid walled, slide-in truck camper using a 3500. I'm coming from a Tundra that gets 13-19 MPG. Those are very reasonable numbers when comparing your HD trucks to my Tundra.

Anyone seeing better numbers if they put on a tonneau type cover?

Single rear wheel or dually?

Edited September 25, 2023 by Another JR

campah · September 25, 2023

I'm looking for a single rear wheel. Trying to stay under 2700-2900 pounds.

Another JR · September 25, 2023

I bought mine with the front camper springs option. I ended up switching the front springs back to the base springs for my model because my camper only puts 100 lbs static weight on the front axle, and I didn’t like the pitch up effect of the front suspension response being stiffer than the rear. If you get into considering camper springs I can offer advice based on my experiences.

campah · September 26, 2023

Hey Jon,

Yes, I am most likely looking at getting the camper package, which should come with the heavier front end suspension. From what I am reading, it will help with breaking when carrying a heavy load.

Was the ride uncomfortable when you weren't carrying your camper?

Pryme · September 26, 2023

20 hours ago, campah said:

Yes, I am planning on hauling a solid walled, slide-in truck camper using a 3500. I'm coming from a Tundra that gets 13-19 MPG. Those are very reasonable numbers when comparing your HD trucks to my Tundra.

Anyone seeing better numbers if they put on a tonneau type cover?

My last truck was a 16 tundra owned it for over 5yrs. Tundra got only 1-1.5mpg more in most situations. Sometimes it’s just splitting hairs. I watched both closely on trucks display and both with a scan gauge.

UWSkier · September 26, 2023

No truck campers in that thread but a few of us with this combo have chimed in there. I've really grown to love my truck.

Salzette · September 26, 2023

Without a camper getting around 12.5 on my crappy short city drives. Considering most of those have been no further than 2-5 miles with about 4-8 stoplights along the way, it’s not as bad as I thought it’d be…

Highway drives have been limited so far but been around 16-19 on those.

Another JR · September 27, 2023

On 9/25/2023 at 5:13 PM, campah said:

Hey Jon,

Yes, I am most likely looking at getting the camper package, which should come with the heavier front end suspension. From what I am reading, it will help with breaking when carrying a heavy load.

Was the ride uncomfortable when you weren't carrying your camper?

I wouldn’t say the ride was uncomfortable (for a 1 ton truck) with the stiffer springs, but the unloaded ride is noticeably stiffer with the the camper springs. I ordered my 2021 3500 cclb with the camper springs (not plow package) rated at 5600 FGAWR. The base springs would have given a 5200 lbs FGAWR.

More important to me than the stiffer ride, the rebound response of the front suspension with the stiffer springs was faster than the rear suspension. This caused the front end to pitch up when going over dips at highway speed. It was worse with the camper on because my camper puts very little weight on the front. It might have been curable with different shocks, but I didn’t need the weight capacity and I wanted the softer ride. I bought the 5200 lb springs and swapped them in.

The camper springs did make the truck stiffer in roll, which would be a benefit with a hard sided camper’s higher cg.

I would suggest researching the weight and fore/aft cg of the camper you are buying, and then calculate the load added to the front axle by the camper. If it doesn’t add at least 300 lbs to the front axle weight I’d stick with the base springs.

On the other hand, if you think you may wish you had bought them, go ahead and buy them. It only costs $600 plus labor to change them and it’s an easy job. I’d rather have the higher axle rating on the data plate with lower rated springs than vice versa.

MORSNO · September 27, 2023

When loaded with a hard sided camper expect a drop in mileage to around 9-10 mpg on average with a gasser, no matter what brand gas truck you get. If you get strong headwinds expect much less. I'm happy on really long multi week trips to get between 9.5-10 if I keep my highway speed down to 65mph with my previous generation truck with a 6.0 and 6 speed.

FreakBeast · September 28, 2023

On 9/24/2023 at 9:46 PM, campah said:

Hey All,

This is my first post and I'm glad I found this forum. I'm considering a new '24 GM Sierra gasser with the 10 speed Allison transmission. I looked through quite a few pages and couldn't find a thread pertaining to MPG on the new 6.6L with this tranmission configuration. I'm looking to use the truck for a hauling a truck camper and I haven't owned an HD struck before so please pardon my ignorance.

What MPG have you been getting on the freeway and also around town? If you have a truck camper, what have you been getting unladen and laden?

If you came from a previous 6.6l gasser with less gears, how has this been doing in comparison? Was it worth it for the upgrade (as I'm also considering a used truck).

Thanks All,

Matt

Welcome Matt

I recently joined looking for info on ordering a new gas HD. Check out the ordering info posts on here if you do decide to go new.

Check out “Fuelly” on the interwebs. It’s a site where you can track and research real life logged fuel mileage for different vehicles. Won’t get you info w camper but it’s pretty cool because it is real data.

FB