Hi, my 92 loyale has been really weird. My automatic shift is not working properly. When my car was working properly, the automatic shift went from 1st gear to 2nd at around 2000rpm, 2nd to 3rd at around 3000, then stayed at 3rd. But with it not working, my 1st gear doesnt shift until the rpm is at 3000, then it wont shift into 3rd gear not matter what and it's rumbling all the time. I've checked the transmission fluid, and it's okay, and I tried going through the manual. What's wrong with my car?