Would be good to know the fuel pressure at both points. Heard those 2004 5.4 up don't have a Schrader valve on the fuel rail. Needs a specific "T" fitting that is in some fuel pressure testing kits. So I have heard.
Well ill change the plugs tonight see if that helps if not put a filter on it then go from tere Tap Tap
It wouldn't hurt to check the compression while the plugs are out if ya have resources to a compression tester.
Sounds like the fuel sending unit maybe if it has b 1 and 2 lean. Not enough fuel equals lean my 2 cents
