I bought a 1998 C3500 with the 5.7 Vortec. I replaced the spider injection, complete fuel pump assembly, fuel filter, the pressure regulator is also new. it will fun fine for a few minutes then I can watch the fuel psi drop out to absolutely nothing. It will hold pressure when i turn the key on. It holds pressure when its idling. but once you get up to speed you can ease into the throttle and the psi gauge starts to fall the more you get into it. i am at a brick wall and advice would be very helpful.

 

Hey man! Was this the problem that prompted you to replace all these things? Did you get a base line fuel pressure reading before the pump change? Possible bad out of the box part? I ask that because I've had it happen to me!