I was wondering how much horsepower can a automatic 1990 gt transmission hold?

 

Looks like nobody is going near this one. I had a 90LX with an AOD, ATI Procharger on a stock motor early on 10lbs of boost maybe 300 HP and FTLPBS. The tranny was fine with a shift kit and correctly adjusted TV pressure as long as it was launching, shifting, stopping only. A couple of "kickdowns" from overdrive to 3rd on the highway and it would fry the OD band (which I think was also the reverse clutch band if I remember correctly)... I had a rebuilt a couple of times with heavy duty bands and modified valve bodies and it held OK but eventually it would go out again. I'm not sure the technology was there at the time for the AODs.. shortly after I switched to a C4 (along with ported heads and big cam) I started to see TCI, Cheetah and some other companies come out with some built AODs that supposedly handled 1000 HP.. it was too late for me, just dropped the rear to 3.08:1 (had gobs of torque anyway) and stuck with a built C4. Doesn't really answer your question other than not a whole lot more in stock form but can be built to handle whatever you throw at it.