most likely transmission gear sensor.
Does your key come out of your ingintion when your in "park". I will shift to park, but the light on the dash for P won't come on, so until it comes on my key is stuck, reverse does the same thing too sometimes, especially in the cold, I need to get that fixed, but i heard its 50+ labor, and i don't see it as a big issue right now, but I also noticed i can have the key turned all the way, but with the engine off, and still be able to shift all around if foot is on the break, so I don't know if thats related or what.