loss of fuel pressure?

i have a 88 k1500 5.7L. it has been acting like the fuel pump was cutting in and out, it'd go from smooth, responsive throttle with plenty of power to, out of nowhere slow throttle response and not enough power to pull itself up a small hill. i changed the fuel pump sending unit tank straps and lines along with the filter, idle air control valve and throttle positioning sensor, new plugs, wires, cap, rotor, and coil. Still doin it...what now i'm out of ideas

figured it out...one of my injectors isn't working