'04 with 150,000 mi. Started , ran for a few seconds and quit. wouldn't re-start. Changed filter, primed, ran for half hour,then no re-start after it sat. O rings good on filter & no leaks there. After working on it today , it doesn't seem to hold prime pressure . When I pump filter I can hear a "hissing" sound on drivers side rear. I don't see any wetness in that area , but could it be an injector o ring or gasket ?
Any Ideas ?

My guess is not the injectors leaking, but a low-pressure fuel fitting. I am not familiar with the exact fuel routing on these trucks, but I would investigate the source of the hissing. Odds are, it is external to the engine. Once that is taken care of, the loss-of-prime issue should disappear.

Thanks for the help. I plan on trying to put slight pressure to fuel tank & check for leaks.
This forum is cool !

if you hear a hissing noise while pushing the primer it will be a low pressure leak i would look at the fuel lines from the filter base out to the ficm and so on

i agree. check for a air leak somewhere either where the lines attach to the top of the fuel tank or where they attach to the fuel radiator.

I would check the two lines on the driver side were they hook to the top of motor the rubber hose inbtween the metal ond the hook up. I had a pin hole on mine in right in the rubber. Thats my 2cents.