From what I hear, the difference in mileage between the 6.0L and the older 7.3L is not that great. Average numbers I hear are 13-16 with the 6.0L in combo driving, 12-14 pulling and up to 18 or so in strictly highway driving. Some do better, some worse. The 7.3L on average seems around the same, perhaps 1/2 MPG better on the highway but with much more variability. My highly modified 7.3L does a fair amount better and has LOTS of power. From those I have seen, the 7.3L seems to respond better to modifications, both from a performance and fuel mileage standpoint. My friend, the local JD dealer has a 6.0L that he drives daily. 12 mpg is his in town average, but we live in the mountains and this time of year it is pretty cold here, which hurts mileage. I know that you are asking for information's sake, but basically most of the diesels in trucks get about the same mileage. Dodge Cummins engines perhaps a little better, but one would seemingly have to drive about five million miles to notice a major savings on fuel. I know folks well who have about every major brand, and they all tout numbers that are about the same, except those that say their one ton duallies are getting 35 mpg's. We are know those people. I would feel pretty confident in the number ranges above, but of course, some do a little better based on driving habits and engine/drivetrain variability.
John M
