Transmission Help - Going back to Park

[Legokcen]

Good afternoon. I've searched for options and started diagnosing, but would like some feedback and next steps. X5 is an '08 3.0 with 57K.

It rained hard last night, I don't know if that'll do anything as it hasn't before, but this being 2020, you never know, so I am mentioning it.

I got in the vehicle this morning to run an errand. Started up just fine and I switched into Drive fine. I lifted my foot off the brake to coast down my driveway and noticed it was barely creeping along. I gave it some gas and it started a bit but felt sluggish. I put it in reverse, came back, having never left the drive and put it in park. Turned it off and then back on again and now when I switch D or N, it swaps back to Park immediately. It has done a few different things this morning:

1. Gave me a "Trans Malfunction - Transmission position P may not be possible. Set parking brake when completely stopped" warning.
2. Then it would stay in Park and would immediately go back if I changed to D or R.

While searching online, I disconnected the battery and reconnected it to try to reset the codes/transmission. I have a Check Engine light now with P0015. I'll swap and clean the sensors to see if that goes away, but that shouldn't be the transmission. I'm still getting the issue where it goes right back into PARK.

Still, engine starts just fine, revs just fine. When I switch out of Park, to any gear, it goes right back in PARK. I've checked to make sure doors are closed, seat belt is fastened.

I'm at a loss now and could use some help please.

Thanks in advance.