Truck information:
2002 Dodge 2500 QCLB Cummins 5.9 with 6 speed Manual. 129K miles
Bone Stock except for fass fuel pump located on side of engine block.
Fuel level between 1/4 to 1/2 tank.


I purchased the truck back at the beginning of December, truck ran great, lots of power. Three weeks ago I went to get on the highway and truck began spitting and sputtering at 2500 RPM, no issues under 2000 rpm. Drove truck the rest of the way home taking it easy. Assumed that plugged fuel filter was to blame. Change filter, bled air as directed. Truck started up, ran great, took for test drive, and was worse than before. Limped back home. Using a fuel pressure testing gauge connected to the shraeder valve was reading 10 psi when bumping starter to energize LP, as soon as truck was started the fuel pressure would drop to 1 PSI. Decided the LP was shot and ordered a Raptor FRRP. After installing the Raptor I was unable to get it to prime. Tried many many times. Finally came to the conclusion that the polarity was backwards on the Raptor. Snipped harness connector wires, flipped and shazam, the Raptor primed and supplied fuel to the IP. After bleeding air for a really long time I was only able to get 1 PSI when bumping the starter. Just to be on the safe side, I tried a second gauge to verify that I didn't have a bad pressure gauge on my tester. Also, reinstalled my old Fass pump which primed immediately and supplied 10 PSI while not running just to verify there wasn't a kinked line. Contacted Air Dog, discussed pump with tech and they mailed me a replacement. While waiting, I did quite a bit of research on the fuel system. Ordered a Vulcan big line kit with pump relocation bracket. Mounted new pump just ahead of fuel tank, and ran the new 3/8" hose with quick connect to top of tank, 1/2" from pump outlet to stock fuel filter and from there to the IP. Also installed a ISSPRO mechanical gauge with isolator at same time. After bleeding the system I was only able to achieve 5 PSI when bumping the starter. Decided that due to the larger volume of fuel line I should adjust the FRRP a little higher to accomodate the needed volume to maintain correct fuel pressure. After adjusting, bumping the starter fuel pressure goes up to 15-18 PSI. Truck takes a long time to start, once started runs smoothly, but fuel pressure begins dropping as soon as truck is running. Fuel pressure will drop to below 5 PSI so I shut it off as soon as it hits 5. In addition, if I bump the starter the fuel pressure rises 15-18 as mentioned but as soon as the pump times out, it quickly drops back down to zero. In researching I thought that the overflow/return valve could be stuck open/partially open allowing the fuel to go right back to the tank. I pulled it out and tested with air pressure at 10 psi, seemed to stay closed, and at 16 seemed to open correctly. I also gone thru all the fittings/ connections from tank top to IP, no leaks found. I've already spent quite a bit of money on the pump, relocation/big line kit and monitoring gauges. My next resort is to drop the tank/lift the bed and see if I have a cracked pick up tube in the tank (1/4 tank syndrome) or a plugged pick up screen. I pride myself in not being a parts changer to find the problem but this truck is testing my patience. What am I missing????? If it happens to be the pick up tube in the tank sending unit, what is my best resolution? I'd rather not drill holes in my tank if possible.

I appreciate any direction/advise given, sorry for being so long winded, just wanted to get all of the facts out there right up front.