The truck does not have a fuel pump-- did you pump the manual primer on the fuel filter housing--?? If the seals are bad in the housing, it will allow air into the fuel system, and not start. Try pumping the primer and then open the bleeder screw to let air out. Then close the bleeder and pump again. The bleeder screw is next to the pump and is made of plastic-- be careful-- it will break easy.
Inspect the FICM wire harness at the passenger side of the alternator. The harness is tied down with a zip tie, cut the zip tie, open up the plastic loom, carefully check for bare wires. The harness and wires get cut, and sometimes short to ground, by contact with the sharp corner of the FICM bracket. Repair, and insulate with a piece of heater hose.
This is a common problem for the LLY engine. Everyone that has a LLY should check this now!
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