I have a 2007 4x4 RAM 2500 6.7L turbo charged diesel.
My question is while driving to Colorado my gas mileage went from 14 mpg in Texas up to 18 mpg in Colorado. Can someone explain this to me. I thought at sea level you would get the best mileage.

 

Texas just brings everything down.

 

You probably filled up with some "bad" diesel. There is no standard in the US for diesel fuel so some of it varies. When I filled up on the Kansas turnpike my 2005 ran worse, had less power, and the milage went to hell.