I think that thing is staying in second gear as a fail safe for you to be able to limp the car somewhere close, to the side of the road, or home. Idk what transmission you have in the car but it definitely reminds of me stuff that happens to a 4l60 or maybe a 4l80. I’d check your wiring harness for you trans. Especially the neutral safety switch. I know with the 4l60e when you disconnect the neutral safety switch you should definitely replace it AND the connectors that go to it just because when you disconnect them there’s an adhesive that gums up the contacts giving you a crap connection. I’ve had my trans rebuilt in my 03 Tahoe a few times but the rebuilder would reuse the neutral safety switch. So most of the time I cannot start it while it’s in park I have to put it to neutral to start it. I’ve gotta replace it and re-wire it with new connectors. I’d definitely start there checking the harness and connectors whether it’s a visual inspection or a continuity check with a multimeter or a both. That would be a good start. I’m just throwing ideas because I know no history about anything done to your car except the forced induction. Hope you can figure it out and I hope this is super simple like replacing connectors and neutral safety switch. Good luck and I’ll be following this as a new sub.
