My 86 gt 2.8l 3 speed auto drives on freeway at extremely high rpm's

I would do two things. First, can you count the shifts as you accelerate? You should see the RPM's drop each time the shift happens. If that is shifting when you expect it to, then hook up an external tach and validate the reading you are getting from your dash gauge. Above 5000 and your engine would be screaming at you. If it is, take it to a reputable shop to see if it can be fixed without too much $$ pain. Your '86 may be sending you a message to replace her. Oh, how long has this been going on? Did it just start and, if so, does the car act like it always has or is this a new trouble symptom?

I just purchased the car about 6 months ago with 86,000 miles on it, I have put 11,000 miles on it myself. it now has 97,000 and it has run this way the whole time. the thing is on the streets the trans runs fine. it's nice and peppy no slippage or anything sounding bad. it's just when it gets above 55 it winds out, and I don't think the converter is locking up like it should. is it possible someone put lower gears in the diff.(if think that would have been a stupid move since it's only a 2.8l) but have you heard of this before?

Sorry, I can't help but I doubt if it is related to the dif gearing. The trans is the only "smart" thing in the drive train. Sounds like it is either missing a top end gear in the trans and a good shop could probably be your best bet for an accurate diagnosis. Good luck. Fiero's are special cars so I hope you can find a fix and keep it on the road.