Gotta major problem!!

[tough90pony]

I have a 90gt and I have a problem with the engine/i don't know.
When the car is running it with all the sudden the idle will drop and when I give it gas it will miss out horribly. It started in May when we got back from WFC. I raced the car and it was fine but the day after, it acted up. It usually does it after the car is warmed up or if I let it idle too long. I 've tried well at least it seems like everything. The fuel pressure regulator, control module, ACT sensor, TPS, O2 sensors,different coil,fuel filter,fuel injection wiring harness,fuel pump relay etc.. The strange thing is that when the fuel pump primes, there will be a hissing sound under the hood. My buddies cars don't do that, we are dum bfounded on what to do next. I'd appreciate any advice you guys might have. Oh, also put new short block,in thinking maybe it was losing comp. but that wasn't it , that was an expensive expirement.