Welcome to the club. To my mind, a good starting point would be to find someone with an advanced OBD II scan tool that will read and diagnose the transmission control module. If the module is sensing a problem, the transmission may operate in limp mode to try to keep it going. If I were seeing a rev / power misalignment I would be thinking in terms of the transmission clutch control solenoid, but without the scan tool it is difficult to know if the solenoid is being commanded but not responding or if something else is preventing the TCM from activating the solenoid.
As the car is new to you, you might want to consider the potential condition of the transmission fluid and filter. I chose to change mine when I first purchased my G6 and have continued to maintain them.
Just a guess based on the symptoms, I have not had this issue myself. Hope you can get it fixed.
