truck was running like a dream it went hunting and just quit. Have recently changed plugs and wires. Drained gas tanks and replaces fuel pumps, filter, fuel tank relay fuse, in dash tank selector switch, cleaned out air filter. Put clean fuel in engine turns like it has no equal. Used some gas to prime, bled fuel lines, fuel all the way up to injector rails a constant flow of fuel to there however when primed starts idles smooth until prime burns off feathered gas peddle to keep idling cough sputter bang. when I stopped to feather the engine idle smooth again then dies,

 

Does sound like low fuel pressure.
Need to put a fuel pressure gauge on it and see what you get.
Do you have a stock fuel system or has it been modified?