Could be a weak OFV,but,since he says that it does not change with rpm increases I am going to say the factory lift pump is weak.

 

Yea ID say it's the lift pump, mine was

 

I figured my lift pump must be getting weak when my truck had about 260k on it. No reason, I just got ambitious and figured I'd put a new one in. It made my truck faster through weight reduction-it lightened my wallet. Absolutely ZERO difference other than that. Not that yours can't be weak, but I'd definitely suspect the overflow valve first. A 4 hour start time points to bad hoses, as you already know. If you continue to have trouble starting it after it sits for a while, the fuel heater might be leaking air in. Where the wires go into the heater sometimes will let air in enough to cause it to lose prime. I know that the truck was out of fuel, but I figured I'd put that out there just in case you still have some trouble getting it to start sometimes.