That sounds like a bad relay or bad key switch. Can you hear a click when you turn the key every time?

still thinking sensor issues as well if it can shift from park with key off no brake lights etc there is some sensor issue there regardless of anything else (also indicated by lights not turning off) idk how much they cost but if not to much/ to hard a new saftey switch could be a good step...

Yeah. I hear 2 relays click in the fuse panel under the seat when I turn the key... every time.

I asked my mechanic friend about the possibility of it being a bad switch or something like that. But he doubts that considering all of those things (he says) run through the computer.

I'm leaning towards something malfunctioning that'* related to the security system... gut feeling lol

If your hearing the relay click every time then the switch is good. But the relay could be bad. Pull that relay and try testing it.
https://www.gmforum.com/t279561/

So I've come to the conclusion that my car is possessed! lol It slowly started to work normally and now it'* totally fine...for now. It hasn't messed up in weeks. Pops off every time. I really don't know what else to say... I'm crossing my fingers that it NEVER happens again.