do i need a new ecu? Options

[mako901]

My '90 gs-t will start fine and run fine, but after driving it for a little while the engine will stumble and get progressively worse. The stumble will get pretty bad, and the power cuts in and out quite violently. It will have trouble holding a constant speed, but if i accelerate or rev the engine, it runs smoothly.
I've had the fuel pump replaced, but that didn't fix anything. It has new plugs and wires. The latest shop I've taken it to (the 4th shop I've had it towed ) ordered a new ecu and says it runs great with it. Apparently the original ecu was throwing out different codes every time or something like that. Before I shell out a couple hundred bucks for the new ecu, I was wondering if anyone here has any idea what is wrong? I've read a little about the capacitor problem, and mine have never been replaced, but I haven't noticed any rotting seafood smell. However, in the past year and a half, every once in a while the car would randomly stall and only start after sitting for a few hours and then run fine.
Any help would be greatly appreciated!