Im not sure if this is an ECM issue or something else, but if anyone has any ideas I'm all ears.

Okay, I got an 86 TPI 350 IROC (Not the stock motor, was origionally a 305), as of right now I got a nasty issue. After running for about 30 to 40 minutes, the car will try and die as if it is running out of fuel. This only happens though while stopped and idleling. It seems that something is getting hot, because once the car sits for a bit it runs just fine. So far I have changed the injectors, the fuel pump isnt very old, and I replaced the connector at the fuel pump where the wires go into the tank. Yet despite it I am still having problems. I'm not sure if it is a spark, electronic, or fuel issue, but if anyone has any ideas or suggestions, please let me know.