Ram 2500 Cummins the most fuel economical

Sadly, you used to be able to get better fuel mileage and cheaper fuel from a diesel. The epa has pretty much ruined those days unless you can do an emissions delete and chip it. I have a '10 2500 Cummins combo. All stock. My best was 19mpg highway NY to NC. Towing 8k I am looking at more like 8 or 9mpg over the same run. A solid 1.5mpg over my previous 5.7hemi in a similar truck. By internet rumor I could probably upgrade mpg again with the 6.4 hemi.

All of which still leaves me curious about the new 5.0 Cummins about to be released. 310/550 is pretty close to what the big 3 were selling just about 8 years ago.