Posted 9/28/2020 09:23 (#8519330 - in reply to #8519135) Subject: RE: 2007 Chevy 2500HD transmission
If it happens when the trailer is attatched check your trailer wiring. I had the 7 way plug in on the trailer side with a loose wire that was feeding voltage to ground. It caused all kinds of strange transmission problems. Unhook the trailer and let the truck sit and it would "reset" and run fine until I hooked the trailer up again.
This was on an 07 gasser with the 6 speed tranny.
Good luck
Dave