“Service transmission Now, unable to shift soon” message on 2021 Tahoe

[JoeBlobs]

Update:
So I got a call from the dealer and said it was the transmission control module, also the battery was producing 300 instead of the 700 a newer battery does and my front brakes are extremely low at 14% life. Which I didn’t even take it in for. Researching a bit more before I call them back and tell them to F off. $1200 for the transmission module.

I would tell them to just replace the battery and don't touch anything else. See how things go after that.