I had a similar problem with my 89gt that it would run ok when cold but as it got up to temp or I drove it for a little bit the damn thing would try to die and if you gave it gas it didn't do anything. The problem started out slowly but ended up leaving me stranded one day.

My problem ended up being a bad inner peice of the dizzy. I beleive it was the stator? Either way when it would warm up caused all sorts of hell. That along with the pip controls the fuel pump on the efi cars and was actually stopping and starting the pump when it got hot. That was once of the most pia thing to find I ever had on that car, bet I spend 3 weekends fiddling around with it before I got it narrowed down.

Hope that you get it figured out.