Lets see, the fuel goes up from the in-tank pump, to the primary/water separator filter, then across the front of the engine to the low side of the IP. From there it goes to the secondary fuel filters and back over to the high side of the IP (hopefully with the FDC bypassed), goes into the Hydraulic Head which then sends fuel to the injectors. The fuel not used by the injector is routed out and returns to the low side of the IP. You said fuel is getting to the IP, so is it getting to the secondary fuel filters? If it is, then maybe loosen ONE of the lines going to an injector and see if you are getting fuel there. Tell us what you experience and fellas with a lot more expertise that I'll ever have can guide you further!