Transmission Problems

I have a 1992 Mitsubishi Eclipse and I have replace the transmission three time in a month. Each time I replaced the transmission, I would work for one day only. It worked well while I was driving it each time, but when I turned it off and let it set over night or a long period of time, it wouldn't pull out of it's tracks from that point on. I would appreciate any and all help on this issue.
Thanks,
Southern

not sure what's going on with that but.. mine just decided to quit woriking at 70mph on day... shut it off and it would go again, maybe a mile maybe a day.??? found out there are relays on the firewall behind the master cylinder. the third from the left is a tranny relay that talks to the ecu.. replaced that for $7.00 and no problems since.. worth a shot..!