Ive got a 2006 6L80 vette that keeps going into some sort of limp mode once it hits 4th gear while driving. If you dont let it get up to 4th it shifts normal up to 3rd and back down to first, TUTD works as well 3rd and under. Once you hit 4th gear the trans will not shift back down or up and just stays in 4th until you park the car and key off and start it up again. If you let it get to 4th, when it sticks you can move the shift selector to Sport, hit the paddles to get it into TUTD mode, put it back and drive and then it will downshift back to 1st when you come to a stop. You can also use TUTD mode to make it shift to 5th or 6th once you hit 4th but it will not downshift and will stay in 5th or 6th until put it back into drive and come to a stop.
I have tried flashing every module i can touch back to stock with a MDI to start over fresh and the problem still longers. The IMS switch and ECU have been swapped out, wiring checked, shift cable adjustment, etc..
The other issue is that I can not do a CASE learn on this car either as it always give me the error of the car not being in park or nuetral but both TCM and ECM register that the car is in park or nuetral and all other positons register as correct like P, R, N, D6, D4.