Need some help/advice on an 8L90 issue. I've installed an L86 8L90 combo from a 2017 vehicle into a square body Chevrolet pickup. Engine runs fine, but having an issue with the transmission. It seems to take off in some gear higher than 1st gear and doesn't ever shift. I can command a different gear using the scanner and it doesn't change anything. I'm able to read vehicle speed, transmission input/output shaft speed, gear selector position, etc using the scanner and everything seems to be working on those channels on the scanner. I can unplug the TCM and it goes immediately into limp mode, I know that doesn't mean anything, I just wanted to do that test to see what would happen.
I've not unlocked or licensed the 8L90 TCM, so it's configured as stock. I am aware of the process of sending these TCM's in to unlock, etc but as I understand that is only required if your wanting to modify the stock tune on the TCM which I am not
is there any other tests or tricks to try to diagnose what's going on here? I'm hoping it's not a mechanical failure but anything is possible here.
Thanks for the help guys