Hi all, newB to the board, but I wanted to jump in on this one. I think 2003dmax6701 and I may be having the same/similar problem and I hope we can help each other. I've been told it's my CP3, but I don't think it fits, I should see other symptoms. I also have no codes. There is no smoke. I've got a 2003 as stock as stock gets with about 122k, had it a little over 2 years. There is no hard start, cold, hot, sitting for 2 days, fires right up. Idle is perfect, there is full power off the line, until you load it up over time. It is very predictable and repeatable when the problem occurs. Starting from a stop up a long medium grade, there's plenty of power, and you hold the throttle at a steady position, about 1/3 mile up the grade it feels like you dropped your foot off the pedal. Pump the throttle, no response, let it idle for 15-20 seconds (by then you're about stopped on the hill) and it has plenty of power to keep going. If you stay in the throttle when it loses power, it will cough and sputter and die. Only light on the dash is the batt light when it finally dies. Then it's a long hard start. First thought, air in the line, I pulled apart the primer pump and the seals looked and felt rough, so I ordered a filter head rebuild kit (AP0029, I believe there's vendors on this board with similar, could probably get it to you faster...). I lubed the seals with 90W, put it back together, then it wouldn't even prime, couldn't get the truck to crank. I thought I had it, but waited almost a week (guess how easy it is to hitch a ride to work at 4:30AM?), rebuilt the pump and when priming it shot fuel to the radiator. As long as I've owned this truck it always just trickled out the bleeder when I changed filters. Also changed the fuel line in/out of the filter housing (about 18" of 1/2" fuel hose). Back on the road, same problem, no better, no worse. Turns out I fixed A problem, but not THE problem. My truck runs great as long as I don't go too fast or uphill. 2003dmax, the trick is the fuel system is under a vacuum, so a small leak will not spill fuel, it will suck air. Just order the seals BEFORE you pull apart the primer pump the check them if you go that route next.... new seals are $15-30, new pump/housing is $600, it's easy to rebuild. I don't think the '03 has a lift pump, someone correct me if I'm wrong. I put a hand pump on the fuel filter drain with it closed, pulled and held ~20" vacuum, so it doesn't appear to be leaking, but found a new one for $17 and got it on the way, kinda grasping to make it to work at this point...
did you change the filter?