91 chrysler imperial

i saved this car from the scrap yard hopefully i did the right thing! when i got the car it was stuck in limp mode(only gears that work park neutral and 2nd), wasent drove for some time so all the codes gone. Anyways i changed the trans fuild and filter, and i should say when i checked it before buying the car it was overfilled i mean dip stick to the rim full. so i drained it and replaced the filter. now it still has the same problem and + it slips out of gear some times into neutral now(in both reverse and drive it slips outta gear). so im stuck on what to do if i spend anymore money on it and can't fix without putting it in the shop ill lose my money. i have $300 in it all the power windows lights radio all everything works motor runs good needs a tune-up but other than tran problems its an ok car was going to resell it and make a few hundred. i was feeling like it was an electric issue at the start but really at a loss now. i still think i could scrap the car and get my money back and run! any help would be greatly appreciated.