Stalling under high throttle

[DJ31499]

My 1990 K5 has been having issues with backfiring for the past couple of months. Originally, I had a trouble code for the EGR valve/solenoid and got the solenoid replaced, helped keep the backfiring down for a little while but it was back in a few weeks. It happens at highway speeds of 65-70 MPH, between 2000-2500 RPM's, under heavy throttle (going up a hill, trying to speed up to pass someone). The engine almost 'pops', cuts out for a split second and keeps going. This week, it started doing it several times after driving up and down several hills on the Merritt Parkway. Next time i took it out, the engine fully cut out/stalled going up these small grades/hills at only 25 MPH. I was pretty low on gas at the time, which makes me think that it has something to do with the fuel pump, could be not sending enough fuel to the engine and it's starving under high throttle. But it could be anyway, the truck sat for an extended period of time before I bought it, so plugs, wires, cap and rotor, etc. I'm looking for some help on what to look for that may be the problem. Thanks!