leak down (cracked fuel line, leak in the fuel pre-heater, & overflow valve)
what the check valve does is stop the reverse flow of fuel back to the tank
vacuum leaks can be hard to find
much rather chase a high pressure leak (wet fuel line, wet fittings, & extra dirt migrating to the area)
frustrating problems enough to make the pope cuss!!!!!!!
how does the truck run once it starts and clears up?
does it start better for the rest of the day?
excessive smoke?
run smooth?