you didnt answer the question. what is fuel pressure?

what is it under a load
what is it idleing?

Fuel pressure is 21-24 at idle and when I shut the truck off it decreases slowly to about 4.

what is it under load? 4psi with the engine running or shut off?

under load you should be in the 30's 24 at idle is pretty good.

4 psi shut off. Couldn't tell under load because the gauge wasn't long enough. I just moved the throttle with my hand and it was like 36-37.

Im starting to think the fuel is draining back into the tank and not staying in the line.

I begining to wonder if your experience my be a cracked ot loose pick up tube ... .... if you have the time ... loosen bed .. on the right side and disconnect bed on the left side ... use a cherry picker to pick yp bed @ corner pocket ... pull sending unit and all and inspect for cracks in pick up tube ... :tu:.... had to do this to a gasser ... was a ton easier than droping tank or pullin bed all together :s:

The pickup tube is brand new

huh ... odd :humm::humm::humm:

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mabye take the check valve and place it between the return and the tank ... flow twards tank .. shouldnt open unless thiers about 5-10 psi of pressure behind it .. :c:

I put one on already.

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Im starting to think about putting a small lift pump in just to keep pressure in the line with the key on.

ok .. did you make the intake side of the LP bigger and the return also ?

I beleive the return side should stay factory sized .. to help with return pressure for this exact reason ... just a theory i was thinking about ... :humm:

Yes intake side is bigger. Return line is stock.