Tow Haul.......When?
2003 GMC 2500HD pulling a roughly 11,000 LB 5th. Would you leave it in Tow/Haul on flat/level highways? Or do you put it in t/h and leave it?
Forum Discussion
Hannibal wrote:
In 2003, tow/haul may have been the new name for O/D off. If tow/haul locks out O/D in the '03 GM as it did in some Rams in between O/D off and real tow/haul mode, it could affect fuel mileage and I would be inclined to turn it off on flat no wind roads.
The OP doesn't mention which engine/transmission he has in his 2500HD, but since he's towing 11,000 lbs I'm assuming he has either a Duramax or an 8.1 gas with the Allison transmission. Tow/haul both changes shift points and enables grade braking on this transmission. It does not lock out overdrive. On the 4L80E with the 6.0 gas, tow haul changes the shift points and also does not lock out overdrive, but there is no grade braking. The 4L80E selector has 4 positions, so to lock out overdrive you place it in "3". I used to have a 2500HD with the 4L80E and observed that the trans actually ran a little hotter with T/H engaged, but I never towed over about 6,000 pounds. FWIW, the manual recommends T/H for loads exceeding 75% of GCWR.
