1995 Geo Metro Automatic Transmission low/rev slips?

Mom just had a salvage transmission put in her 95 Metro and it does the same thing. If the solenoids are internal-saw that in a previous question-how can both have the same problem? Is there a relay or if there is a TCM can it be flashed? Fluid and filter changed on both transmissions before and after installation of course. It has the 1.3 four cylinder with A/C and no other problems.. PLEASE HELP... Mom loves this little car and refuses to part with it.