22.14 mpg on my most recent fillup. With GDE tune, winter diesel, no fuel additive. Half city, half highway, plenty of bad traffic, portland area. Accelerating just as quick or quicker than traffic (So not babying the throttle). Along with, I'd estimate maybe 25 judicious uses of full throttle or launches from a stop on this tanks worth of fuel as traffic/safety situations require. 57-64mph on the highway, usually cruise locked at 57. Pleased with these results. I can't always accelerate like a granny and feel like an asshole if there's someone behind me. I get down to 18mph when I'm driving it like a racevan. Oh and the load, well hmm, half of this tank had about 600 pounds in the back, half of it was unloaded.
04 2500 high top 140" wheelbase, michelin LTX AT2 16" tires, recently changed synthetic diff oil may have helped, engine oil is mobil 1 euro formula oil 0/40w