I actually checked mine today. Dodge 2010 6.7 3500/1 ton 4wd 4-door cab with full 100 gal transfer tank in bed, around 13k on odometer so far, about 200 miles half interstate at 65-70 mph, half other roads at 45-55 mph, some cold weather idling to warm up: 14 mpg. This is with the new auto transmission. I had the engine brake on for most of this check if that has any effect.

That is about what I would expect for this large and heavy a truck. This is THE best truck I have ever had. In my opinion, there is a reason this particular 3500 combination was the Motor Trend "Truck of the Year" for 2010.

If you are looking for a heavy duty working/highway truck I can not imagine anything better. 

On the other hand we also recently purchased a 2010 Dodge Ram 1500 std cab, 8ft bed, auto, 4WD with a small 4.6L gas with air rear shocks and a neat aluminum topper in back as a shop parts-run truck and that seems like a very nice combination for a lighter duty more economy truck for lighter loads and shorter/non-trailer runs.

Everyone who has driven that gas truck so far really likes it - prefers it to the diesels for around town.  I don't know what the gas mileage is on that one yet but it seems like it does not use much gas.  Much better interior details than Dodge used to have, even in this basic industrial low trim cab. Still a good drive train. Big tires which I like.  

I think that folks would be much happier with a truck if they bought gas engines for most applications and diesels just for where the highway/towing/hauling benefits of a diesel are required. jmho.

Jim at Dawn