Truck Repair: N14 difficult to start, fuel pressure, tank

Question
We have a N14 that once started runs great, but takes 3 or 4 hits on the starter for several seconds to get started.  We have also needed to hook up a booster to give it additional juice to keep it turning over.  We have changed the fuel shutoff and confirmed voltage at shutoff as well as adequate fuel pressure at injec. pump.  Truck has been at a dealer for 3 weeks now and no answer. Any ideas?

Answer
i would like to say without seeing it i know whats going on but i cant.. the only thing i can think of is something is bleeding fuel out of the system or back to the tank and your losing prime.does it smoke after you get it going or during,you might have a injector leaking down after shutoff let me know i like to help more.thanks