C1500 idle

1996 C1500 chevy p/u, 305 engine, auto tranny has idle problems. starts and runs and idles fine when engine is cold. after engine is throughy warmed up it won't idle after warm startup without giving it some gas. just started doing this about a month ago. had the fuel pump in the gas tank replaced about 3 weeks ago b/c it quit working, but the warm startup idle problem was there b 4 and after the fuel pump replacement. any clue as 2 what could be wrong with this warm engine startup idle problem?

egr valve.

I would'nt automaticly say EGR, if you check some posts you'll see that there are several posters with the exact same trouble, including myself, I have gone through my egr system, checked ---rechecked sensors, the iac, and still i scratch my head as it ldles like crap, but runs down the road perfect,
all i can say is start testing before replacing, and good luck