Hello I have been chasing my intermittent power problem for a couple of years now. I think I finally came across the culprit. I just had the pump looked at for the second time.I installed the pump and the truck ran good for about a week and than started acting up. I serviced engine and in doing so removed and inspected the fuel heater. assembled everything and installed gauges for checking pressure and restriction. Check gauges. shut engine off to adjust valves and check for bent push rods. I was looking for anything to give me my power problem. Adjust valves and truck would not start i had to bleed system to start shut truck off again and again would not start and filter would be half full( I read threads on this in the forum) installed check valve on lift pump no help filter still leaks down. Keep in mind I have never had a hard starting problem just a intermittent power problem. while checking filter i noticed fuel on fuel heater plug. I removed heater again and inspected gasket it was deformed and I used a straight adge to see if it would seal, just barely. I disturbed the 13 year old seal so I replaced the seal and no leaks truck fires right up and runs real good and fuel filter is full. I think this might have been my problem from the get go , air was entering through the seal but there was definitely no fuel leak before I disturbed the sea and the truck ran horrible before i replaced the seal and it runs good after . I am not saying this is the problem but definitely something to look for and replace.
Things that I have done before this was every thing but overhaul the engine from the fuel sender in the tank to the injection pump twice except the seal. It was a good thing to because the pump had a broken spring for the plunger and was making metal so I guess I dodged the bullet by having the pump looked at for a second time at a different place.