1990 Buick Regal Sputtering/Stalling

Engine Performance problem
1990 Buick Regal 6 cyl Front Wheel Drive Automatic 102k miles

I recently purchased a 1990 Buick Regal Custom with a 3.1L V6, and I'm experiencing a problem after it's been running for about 10-15 minutes. The car will hiccup and sputter like it's running out of gas, and won't crank up until it's been sitting for about 20-50 minutes. The fuel pump engages whenever I turn the key, but I don't know if it's trash or something else that's causing it to malfunction after it's been running for awhile.

Also, the Schraeder Valve on the FI system consistently has air building up in it, regardless of how much air/fuel releases from it when the engine is off. Is this a problem with the Fuel Regulator? I've also been told it could be the EGR Valve, but if that's case, would it also be the cause of the air in the Fuel Rail?