Thoughts on frustrating situation.

I actually just had that same vehicle in my shop with somewhat similar situation. These vehicles have a known issue with the Transmission Control Modules causing many problems, including the locked in gear situation you seem to have encountered. I have not seen a transmission failure, necessitating a full rebuild though. You didn't mention mileage on vehicle, though. I guarantee the used car dealer became aware of the prevalent transmission issues soon after he bought it. The dealer is also well aware of these issues. I think there may be a class action suit underway. I use Snap On scanners, and they do tell ( on some vehicles) how many miles have passed since particular code was cleared, but obviously, not time or date. Dedicated Chrysler ( Stellantis) scan tool may be able to display that data. Good luck.