I have a 1994 mercury sable with an axod E transmission and its stuck in 3rd gear but if you manually down shift if goes to 2nd and first. But it won't shift up by itself. You put it in drive its in 3rd and if you stop at stop sign and go its in 3rd.
What I have tried lucas trans fix but that doesn't do anything.
Have a trans pro give it scan and pressure check. Chances are the transmission is bad and needs replacement. Don't forget the replace the radiator if you do, it keeps metal contamination from the new trans.