Disengaged Tow Haul Mode

[James Beyer]

Hey all, going up I-75 towing the Rockwood TT, 9000 gvwr, with our 2024 gmc 2500 6.6l gas at 65mpr. 

Stopped at a rest area for a few, started back on the highway about a mile, the truck jerked, disengaged tow haul mode, and went from 2200 to around 3800, noticed the check engine light on, then the air conditioner was surging. Any Ideas what caused this?

Later-

Edited Friday at 09:31 PM by James Beyer
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[davester]

you would need to get a code reader and check what codes the ecm is generating.  I would use one that can also get tcm codes.

[James Beyer]

Well, coming home from the UP I used the manual or column shift and set up to 10 gears, without Tow Haul Mode, and it worked good.  One 75 mile stretch I averaged 9.9 mpg with cruise set at 65.  Still have to figure out what is wrong with truck but happy that manual shifting is an alternative instead of damaging the engine/transmission,

Later-