Hi There we just swapped a 4l80E into a 2007 GMT-900.

We added the ISS and made the wiring changes. The truck will shift 1st, 2nd and 3rd but never into 4th even if I use the scanner to select 4th gear.
The OS loaded is the 2008 Express van 24239927. If we manually ground the solenoids it does go into 4th and we double checked the wiring.
So at this point it looks tune related but can not find the issue. I also loaded the OS and tune out of our 2014 ZL1 that has a 4L80E and it does the same thing.
Does anyone have an idea of whats going on?

Thanks

Nolan