This is a 94 bird and from what im told,, again "im told" , the codes were pulled on the tranny and none showed up. Im not confident in the users ablity to pull the codes but thats a different story.
Problem......
owner says it will shift from 1st to 2nd then D and OD just slips and the tac verifies it cause its pegging like its in neutral.
mileage is about 80k and the person who pulled the codes thinks its a torque converter problem. He also mentions that its a "two stage" transmission,, what ever that means or bearing it has.
AOD or AODE???(I'm assumin its a E since you mentioned readng codes). There is a clutch in the converter that engages for lockup/OD operation. So yea it could be the converter...
If its a AOD the O/D band is likely shot... Or if there is no 3rd or O/D the inner input could be broken(got the T-shirt on that one) or the direct clutch is toast... Both problems(clutch/band) are fairly common...
happend to me on my transgo shift kit tranz. never tore it apart to see what was wrong but same symtoms. but im almost sure my imput shaft broke bc i heard some kinda noise at 60 mph like a grind and snap. if it is the shaft the whole thing needs to come apart to fix it . not fun.
(more and more i am disliking these aod's or auto trans. in general)
A 94 Bird, if 4.6L, would have the 4R70W AOD-E. It was known to have a weak torque converter.