I have a '03 Ram 3500 quad cab, with a 5.9 Cummins and a 4:10 gear. The truck is a pulling nut, moving gross weights of over 20,000# on many trips. I started having what I thought was a fuel problem last December, but to date we have not been able to track it down. The truck will run perfectly for 100 or more miles, sometimes up to 500, and then it will seem to begin starving for fuel on big grades, going way down on power. It seems that when it starts this, the longer you run it the worst the problem becomes, sometimes slowing to an absolute craw going uphill. You can pull over, shut it off for a few minutes and the problem will go away for a period of time, or in some cases, will disappear altogether for the duration of the trip.
I have had the truck in the shop on two different occasions, with the computer showing no codes whatsoever. I have been told that it could be the fuel transfer pump, or the computer. Any ideas?