1999 Chevy Suburban Engine Stall & Misfire when pressin

I got gas a few months ago and started having problems with the performance of my vehicle. When I was pumping the gas it took about 20 minutes to pump $40 worth of gas, I am assuming that it was dirty gas. (Didn't realize at the time how long it took until after) The very next day it started lossing pressure going up hill or when you pressed the gas to quickly speed up. And when you let the vehicle idle you can hear a slight misfire. I have tried fuel injector cleaners, Heat for water in the tank and changing the fuel filter. It usually takes about 20 minutes of running the vehicle for this to happen, but you can turn the vehicle off for a minute and then it will run fine for another 20 minutes.

I also replaced the fuel pump exactly 1 year prior to this incident with an aftermarket fuel pump and just in the last couple of weeks my gas gage has started jumping WILDLY! Could the fuel pump be going out again and causing all this or could it be fuel injectors, throttle body or sensors?

Just need some assistance with what to look for before spending about $100 to $150 with a dealer to run a diagnostic test.