So I have a 1987 Fiero GT, and mechanically, it is in absolute perfect condition. I took it to Watkins Glen International today and ran 6 laps at a max of 100mph. On the 3rd lap, I knew I had a problem when it wouldn't go into 2nd gear. It's a 3 speed auto, and now it doesnt shift until 5000rpm, when it used to at 2500 rpm. Once I hit 20mph, it WILL NOT accelerate at all, even with my foot to the floor, until it hits 5k. Is this a slipping tranny or delayed shifts? Or what?

Problem still occurs when driving around town normally.

You would probably have a lot better luck on a Fiero forum.

Yeah I just created an account there, just put it on here for the heck of it.

Do you hear any grinding noises when the transmission shifts gears?

Nope, but after testing the car out a bit on the road, doing some 0-60 runs, I've determined that shifting into 2nd is delayed, and the passing gears slips.

Is is an automatic transmission with a torque converter or a automatic manual with an actual clutch disc?

Turbo-Hydramatic 125 C[edit]
This was a later model of the 125 that debuted for 1982 and included a torque converter clutch or TCC. The TCC acts similar to a clutch in a manual transmission vehicle, in that at speeds above 50 MPH a combination of engine vacuum- and temperature-sensing valves, and a dedicated brake switch - and in later models an ECU - activated a solenoid which engaged a clutch physically locking the impeller and turbine inside the torque converter together causing engine power to be transferred directly to the transaxle. The C in Turbo-Hydramatic 125 C denoted the use of a TCC. The solenoid that controls this is notorious for failure due to overheated plastic componentry, and problems indicated by an engine stall when stopping from speeds greater than 55 MPH. This occurs because the clutch does not disengage, and as the affected vehicle's speed nears zero miles per hour, the engine is forced to decelerate to zero rpm.

This was on wikipedia, pretty self explanatory.

I really don't know, sorry.

Don't worry about it, it's a torque convertor, basically it acts as a clutch for automatic transmissions. The torque convertor is probably your issue and it's acting up causing your shifts to be delayed, I would have to examine it in real life to know more but I would assume perhaps one of your lines or passages has a leak or crack causing the vacuum to drop and hence the delayed shifts. I'm not a certified mechanic but that is my 2 cents.

Also it might be a good idea to check your transmission fluid level and condition.

Did that, it's fine.