The biggest problem with these engines is--- the did not put a fuel pump in the system. They used the CP3 to pull the fuel from the tank, through the filter and into the CP3 where it is pressurized and sent to the injectors. So any small leak from the tank to the engine, and the fuel will get air and allow the fuel to drain back to the tank, resulting a no start.
I have pressurized the fuel tank with the outlet of a shop vac-- be sure it is clean and place a rag over the hose to catch any dust. While pressurized, inspect the entire fuel system, filter, WIF sensor, around the hoses and lines. You can use shop air but keep the pressure below 10 lbs. Hope this helps.
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.