First pop the gas tank open when it starts failing. The tank vent could be failing and causing a vacuum in the tank and shutting off the fuel flow.
If that doesn't seem to help, then you likely have an electrical component that is failing with heat and that will be a bit harder to locate and fix.
Can also be caused by an input vacuum leak when it heats up.
Thanks for the response from you guys. It has Cobra pipes but they were put in 5 years ago and had no problems until last month. I checked the gas tank venting and it still began stalling after about 20 minutes of running. I recently had to change the fuel pump assembly. I also got a new air filter and fuel line. What do you mean by a "input vacuum leak"? i will try EFI cleaner.
If the old fuel pump failed due to debris build up perhaps the tank needs to be checked out....also the new pump may now need cleaning out. Not suer what ER means about an input vacuum leak....maybe he means there could be a leak in the efi circuit?