So I've noticed this a few times in the 4 years I've owned my 94 Z28. When it's warm out and there's lots of stopped up traffic, or if I'm driving on the freeway then slow down on the off ramp, there are times the fuel pump begins to make noise like it's kicking in. The gas tank is anywhere from a half a tank to full, it makes that whining sound that is pretty clear, and then it will shut off, like it's not getting gas. I have to wait for about 5 minutes or so, start it and see if it's ready. If I take the gas cap off it let's out a swosh of pressure. After it sits it's perfectly fine. Someone suggested that I get another gas cap as the one that's on it was off a 94 Chevy Truck. This only happens when it's warm out though. (the engine was replaced 3 years ago and I have about 76k on it. New transmission with 2k on it).
What do you all think?

 

start with a new gas cap. test fuel pressure. pump may be goin. they can get warm and quit then once they cool off they work. lol, drove around 10 miles at a time with my truck for a while.

 

What you're describing is normal. Heat and motion can cause the gas tank to build up pressure. The fuel system is a sealed system, the gas cap does not vent out.