Hard to start and keep running

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The 4.3 engine will start, but dies if i give too much peddle or no peddle (I have to tap, tap, tap the peddle constantly, to keep running). Will not idle stalls out every time. I did check or replace; Throttle sensor checks out ok, Fuel pump Relay is ok, Installed new fuel filter, Fuel pump works, but has low pressure, but i bypassed that with a off-market electric fuel pump (not in tank), but... engine does the 'same' thing when started. Please help