1992 Chevy Truck Fuel Pump

I just replaced the fuel pump in my 1992 Chevy c1500. The vehicle would idle fine but would stumble under acceleration like it was running out of gas. So I checked the fuel pressure at the TBI unit, it was 5 psi. So I changed the fuel filter, that increased the pressure to almost 8 psi, but the it still sounded like it was running out of fuel. I removed the bed, replaced the fuel pump, strainer and inspected the harness inside the tank. Harness looked very good, as if it had been replaced before. Once finished I started the vehicle, it still stumbles under acceleration like its running out of gas. I checked the voltage at the connector outside the tank, it was 8.79 volts, key on engine off. When driving it it very sluggish and even tried to spit back through the TBI unit a little under hard acceleration. The engine idles perfect and revs up fine as long as your not driving it or have it under a load. What else should be checked?