Towing in tow-haul with 6sp auto

[Wintersun]

Can't speak for yours, but my 2012 will go into 6th gear all day long while towing....

And how do you know it is 6th gear? Only way I can tell the gear is to have the trans in manual mode at which point grade control is disabled. According to GM, when the transmission control module detects a downhill condition and activates grade braking it also keeps the transmission from going into 6th. But what do they know. Still I cannot see why you would want the transmission to be in the highest overdrive gear when going down a steep grade, with or without a load, might as well put the transmission into neutral.

 

My LML will rev up into the mid 3000's when going down a steep grade with a load and it is hardly a problem and the way it is supposed to work. Having the trans upshift to drop the RPM's down to 2000 pretty much defeats the grade control and exhaust braking entirely. The engine produces its maximum horsepower at 3000 RPM so having it in this range is not going to damage anything and is well within the redline limit. The engine is also not burning fuel when the torque converter is locked and the exhaust brake is functioning so as to maximize engine braking.

 

GM states that the "Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75% of the vehicle's Gross Combined Weight Rating (GCWR). Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/Haul is recommended only when pulling a heavy trailer or a large or heavy load." That works out to a tow load of more than 10,000 lbs.

 

The exhaust brake only works when the torque converter is locked so in theory it should work more of the time in Tow/Haul mode. What I do not know is what the difference will be in grade braking with a 4,000 lb. load with the Exhaust Brake turned ON, and with Tow/Hual turned OFF as compared to with Tow/Haul turned ON. It is something that I will need to try for myself.

[truck this]

I dont know about the D max but my 1500 6 spd in tow haul doesnt go into 6th in tow haul mode. Next time you guys are on the freeway doing 60+ mph towing nothing behind you press the tow haul button and watch the tach and see what happens to the rpm, mine goes up because it shifts out of 6th.

[johnhankel]

I dont know about the D max but my 1500 6 spd in tow haul doesnt go into 6th in tow haul mode. Next time you guys are on the freeway doing 60+ mph towing nothing behind you press the tow haul button and watch the tach and see what happens to the rpm, mine goes up because it shifts out of 6th.

 

Try it again sometime when you are going over 70 or so. It will shift up into 5th for a bit, then shift back down into 6th... It tries to keep the rpm's above 2000 in T/H mode. So if you are right around that in 6th, it will shift into 6th. I tow my antique tractors all the time in T/H mode on the interstate, and at 71-72 mph I am always in 6th gear...

[Elbert]

As noted up around 70/75mph in tow haul mode it will shift into high gear (6th), I' got where I just use normal drive when I'm on the hwy in relatively flat ground (towing)...4.10 R&P 2500HD 6.0 2014