My car wont shift into park anymore

So it can only be stopped on flat ground and will only start in neutral Honestly, I'm getting very concerned that this time it could actually be too big/costly of a problem to fix, because I feel like my car still runs pretty good, and I'm really hoping its only just a little confused right now.

So, every time I move the shifter into Park, all of the little gear lights will light up, instead of just the one light that corresponds to "P". Then, it will start to roll down even the tiniest incline, as soon as I take my foot off the brake, so it can only be parked/completely stopped on very flat surfaces. However, when it does start rolling, either forwards or backwards, you can feel/hear that somehow the car keeps catching itself over and over until its able to come to a complete stop.

So, then when I stop my car, it still doesn't think that its in Park, so the engine can only start again if I put the shifter into neutral first.

What do you think I should do? Does it sound fixable? Or do you think that realistically I should probably just start looking for a new car? Please & thanks for your all your time and help.