My 1989 GP SE w/2.8L did very similar to yours, a little different, but I'll share just in case it helps.
Mine would start up fine, accelerate fine but after it warmed up or after a long drive on the highway, if I let off the gas, it would die. It would occassionally be a bit hard to start back up but most times would start back up fairly easily. I got to the point, before I corrected the issue, that I would just give it some brake to stop at lights and signs and such but still give it some gas so it would keep running.
I dont recall it ever dying on me after putting it in gear or something like that, but its been a while since I had that car. It turned out to be the crankshaft position sensor.
Ironically enough, when I got my current GP, shortly after getting it, it started to stall as well. Tach would go to 0, sometimes difficult to start back up, other times Id feel it miss a beat then the TCS light would come on and Traction Control would turn off. Turns out, it too was a crankshaft position sensor. I distinctly remember thinking after figuring that out, that after all this time they STILL have problems with that sensor.
