[CamaroBruno]

OK so here are the results, explained as best I can. I'm not a gear head so you'll have to excuse me.

Prior to taking the car in to my dealership, I took the Vitesse off to see if it would fix the issues and while shifting gears seemed to smooth out a hair, the problem was definitely still present. The hard shift from P to R was definitely not impacted by removing the throttle controller.

It turns out the dealership called Chevy engineers who pointed the technicians to some solenoid in the transmission which helps regulate the transmission fluid pressure needed replacing. Apparently the pressure was being held at maximum which either caused gears to slam into gear when changing or not change at all. They didn't have a specific notice for Camaros but the same issue had presented in the same transmission in other models of Chevy cars.

This has completely resolved all of my A8 transmission issues. It even seems smoother now than when I brought the car home. I'll put the Vitesse back on soon, since I loved how responsive it made the throttle. It would seem to me that the throttle controller was not the root cause but because it made throttle input more extreme, it made the transmission issues seem more extreme.