I have a 4L80E transmission that was staying in 2nd gear. Finally
down a DTC 81 that mentioned the 2-3 shift soleniod and the "QDM" as
possible faults. Not sure what the "QDM" is or where it it is located.
QDM = Quad Driver Module...........
it's inside the computer.
If 2nd gear "fail safe" on the tranny is the ONLY
issue the truck has.......then "your" cheapest
"guess" is to change out the shift solenoid and
see what happens.
There are other tests to narrow the diagnosis,
but you don't own the equipment.
change the solenoid.......
that's what the tranny shops gonna try 2nd anyways.