If you own any 1996+ GM truck its worth teh $20 to buy a fuel pressure gauge. The Vortec 305/350 L30/31 run at 60-66 psi for suel pressure KOEO(key on engine off).
These trucks are known to have isses with the CSFI spider poppet injectors.
Does it run better when dead cold. or does it only run crappy after the engine has warmed up?
Could possibly be an O2 sensor or its wiring. A good test for O2 sensors is to get on the road and hold the throttle wide open. If the truck accelerates good at WOT, but runs crappy when at part throttle or cruise it could be an O2 sensor because the O2 sensors arent used at WOT while they are read while at part throttle.