I too have a 2004 600 4x4 dually with 6000 miles on it, automatic and
3.73?s. It has never seen 15 mpg, 14?s on the highway empty and 13?s in town. Dropped into the twelves when towing a single axle trailer with about 3000# gross on it. Real disappointing, since I traded a
99 Cummins dually that routinely got 18+. I was expecting some less but not this much. Came here to see what others were experiencing. Anyone else had experience with a dealer "adjustment" that improved economy? Has anyone seen significant improvement after the break in period? Thanks