I drive two diesel trucks:
Work truck: '99 F350 SuperCab, 7.3 PowerStroke, 2WD dually, 6-spd, flatbed, 3.73 axle, 90K miles on it, 0 problems.
MPG: 15-17, usually in the 15-16 range
Personal truck: '98.5 Dodge 2500, 24V Cummins, 4WD, 5-spd., short bed, 3.55 axle, 127K miles on it, 0 problems.
MPG: 19.5-22, got as high as 24+ a few times
I recommend that you drive a Dodge with the Cummins for comparision with the Ford...especially if you are looking for a manual transmission. Just drive both the Ford and the Dodge to see which one you prefer.
I don't know if something is wrong with the '99 Ford that I drive (its an early-'99, built 3/98) but it is temperamental vehicle. It is difficult to drive smooth. The transmission is stiff and hard-to-shift. Something in the shift linkage randomly binds so as to make it impossible to shift into 1st or Reverse. Its been to the dealer a few times for this issue, with no solution.
To its credit the Ford really handles well. The steering is precise for a heavy truck.
Engine: The PowerStroke is called the "PowerJoke" at work. The engine feels really gutless below 2000 rpms...to the point of being kind of scary when making a left turn into moving traffic. Get above 2000 rpms and it starts to rev like crazy and your quickly looking for the next gear. Sort of a Jekyl and Hyde thing. I think the engine's ECM is detuned in the lower gears to prevent wheelspin.
I know that this comment may start a war, but I feel the Cummins is the superior engine if you want to tow or haul heavy loads...all things considered. This comment comes from a Ford fan. I won't get started as to how great my Dodge has been because this post is long enough.
Another benefit of the Dodge is a tremendous resource on the web called the Turbo Diesel Register. It is like TractorByNet, but it is dedicated to the Dodge Cummins trucks.
Turbo Diesel Register
In stock form, the Ford with the PowerStroke will beat the Cummins in a drag race every time, but I'm not into drag racing.
"Six-in-a-row is the way to go!"