You might try this--if you have a shop vac-- use the blower part -clean the vac first and inside of the hose-- place a clean rag over the hose to catch any dirt-- place the hose over the fuel tank filler tube and run it for about 5 minutes. That will pressurize the fuel system all the way from the tank to the CP3. Now check for any fuel that may have been pushed out. That will show where the system might be sucking air.
(You can use a air compressor, but you need to keep the pressure to about 8 lbs in the tank, The shop vac will not over pressurize the tank)
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.--- Jerry