Here is some info on the "Bottle Test".
On the drivers side fuel rail-- to the back and next to the Turbo, you will see a "U"
shaped 3/8 hose-- remove the hose from the fuel rail-- and plug the hose.
Now attach a 3/8 hose to the fuel rail nipple, and stick the end in a bottle. Now drive the truck hard-- with several wide open runs-- if there is any fuel in the bottle the FPRV [fuel pressure relief valve] is leaking main pressure from the fuel system.
The FPRV is a plug looking part that screws in the back of the driver's fuel rail. Many just increase the pressure with a couple washers, to help hole the pressure. Others use a "Race" plug [not recommended] available from supporting vendors.
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.