Hmmm... This has been a rather difficult one to hit a answer to every time. But I know the Raptor fuel system is nothing but quick connects. Eric over at Vulcan Performance told me about a sealing issues with the suction lines and how the fitting isn't design for suction. So getting to people have one stay in the cab and bump the starter while the other wiggles the suction line fittings carefully. The person in the cab has to watch for pressure fall occur while you jiggle the lines. Now I know you got a digital display so the display might update to slowly to actually show air bubbles. You might end up using a mechanical test gauge for this.
Another way to test is to pressurize the tank and look for wet spots...
Basically as you demand volume increases against the supply volume your pressure will fall. But I know the VP44 only takes about 20-25 GPH at WOT for the injectors the rest is sent back on the return line to the tank. So knowing this you pressure show stay pretty high like myself but if there is suction problems (air leaking in), kink lines, plugged filters, etc.
Oh thinking about that how about the line between the stock filter and the VP44 is that stock or 1/2"???