The Fire Chief for a town in my county bought a 2004 6.0 last year and hasn't done anything to it. The PO did a few updates, but I'm not sure what. Anyway, I just found out he has it, so I'm trying to help get him bulletproofed, etc. Well, he calls me today and tells me he's been having a stumble/miss at random times, and his fuel pressure drops down to about 50 and fluctuates a bit when this happens...otherwise it's steady at 59 PSI. I start brainstorming, thinking maybe it's a fuel filter issue because he never changed them, and has no idea what kind of maintenance it had prior. Then he tells me that while it does this randomly while driving normally, he says it ALWAYS happens any time he is driving uphill. THAT is where it has me stumped. I would suspect fuel starvation, but he said the last time it did it his tank was full, and he's pretty sure the other times it was full as well (he lives about 2 hours from the nearest fuel station, so he always fills up before he goes home). This is new on me. Anyone have any ideas?