The low mileage was because of driving around in Rocky Mountain National park at the high altitude. Diesel's and any vehicle lose power at high altitudes so you probably were having to use a lot more fuel to get it to move that heavy truck around the park. Thats a lot better than what my truck would get up there. I would probably get between 6 and 8 MPG.

As a side note, I have may truck up for sale as well. I don't know If I'll sell it but we'll see. I still need a truck so I am not in a hurry but I want to get something with a little better mileage and lower payments. Who knows, I may not sell it at all. I wish they made the engine more efficent because I love the truck other than the FE.

 

I seem to get the opposite effect with my vehicles. The high altitude reduces the power but increases the FE, I guess from less oxygen and but also less wind resistance. Back in October I drove from Boulder the Rocky Mt Nat. and got a decent 26mpg going there, and an awesome 35mpg coming back.

Same thing driving from Boulder to Mesa Verde in my Element, the best tanks were at the highest altitudes.