Tow/Haul feature on GM vehicles

[Silvertwinkie]

I was looking at the GM site today and found what the tow/haul feature does:

www.duramaxdiesel.com

Go into the Allison transmission section.

Tow haul in essence locks the torque converter after 1st gear to keep the trans from overheating due to being unlocked.

FYI....

Eric

[alan]

I can't speak for the Allison, but in the gas engines, tow/haul simply modifies the transmission shift program to adjust for heavier loads and does not prevent the transmission from dropping out of lockup. In my 03 3/4 Surburban, regardless of whether or not tow/haul is selected, the transmission drops out of lockup based on speed (typically between 45 and 50 mph). It does not drop out of lockup in either 3rd or 4th gear under load (different from light duty vehicles). Increasing throttle position under load only forces a downshift to the next lower gear.

[Jabba]

I checked our gas mileage after our run this weekend, ran it in Tow/Haul mode the whole time and got 15.1 MPG with a full tank of water, 2 full LPG tanks and everything else, I was ecstatic to say the least! It was a mixture of freeway and secondary roads. Can't beat that!