I have a 1995 Ford Probe SE and I have had problems that were like the one that you have mentioned. I found that if the battery terminal is lose or the battery is weak the car shifts
erratically. I have another problem with this transmission as well, it keeps losing fluid through the high-pressure release valve. This also causes shifting problems over a period of time due to low fluid in the transmission. I have yet to figure out why this does this. I have even changed out the valve, which seemed to help for a short time and then started all over again, maybe you can help with this problem. I wish you the best of luck and hope that I have been of some help to you.