RAM 2500 6.4L Towing Observations

I pulled a 12k 5er with a 5.9L Cummins in a 2007 3500 SRW and then the same 5er with a 2014 Ram 2500 with the 6.4L Hemi. The Cummins got 10-12 mpg and the 6.4L Hemi got 7-9 mpg with the same load.

Exactly, 12,000 pounds is getting near the end of the performance envelope for the 6.4 and only about half way for the newer diesels. If you calculate the difference between say 11 mpg and 8 that are the mid points of your experience it is easy to see that the diesel is at least percentagewise substantially more fuel efficient under load.

I have heard nothing negative about the 6.4 and if I wanted a truck to go grocery getting, take short trips, tow almost never or a very small trailer then the 6.4 might make sense to me. One of the biggest problems of all normally aspired gas engines is altitude. In the mountains the power loses about 2.5 percent per 1000 feet altitude. The turbocharge diesel can develop sea level power up to around 12,000 feet. It makes a difference towing a heavy load up the hill.