Ok so this is the weirdest and tbh most frustrating issue I’ve ever dealt with. My TEHCM needed replaced so I ordered a warrantied rebuilt one. Thanks solenoids for failing. Anyway, I got it installed and now....the speedometer stays at zero. And the truck stays in first. So far I have:

flashed the tcm using GM SDS
updated all modules to current using GM SDS

Mind you I was driving this truck every day before I swapped out the valvebody/TEHCM. So the VSS isn’t bad. On the topic of the VSS. When I watch live data in GDS2, the vehicle speed rapidly fluctuates between 10mph and 250+ mph. Also, when driving I can use GDS2 to manually command a shift to second gear successfully. 3-6 I can command, however it isn’t shifting and I assume it’s because of the speed. I’m at a loss on this. All modules show they have the most current software installed, and the correct vin written to them.

vehicle is throwing no codes at all