To each their own. Out of curiosity, I decided to pull up fuelly for 2015 trucks (RAM Ecodiesel versus Ford 2.7 Ecoboost).
For the 2.7 with 56 vehicles and 563 fuel ups over 212,000 miles, they note a fleet average of 17.83 mpg
For the 3.0 Ecodiesel with 159 vehicles, 2,873 fuel ups and 1,288,000 miles they note a fleet average of 22.81 mpg. So about a 5 mpg difference between the two. Depending upon perspective, and increase of 28% more mpg over the Ford, or a decrease of 22% from the RAM. Take it for what it's worth.
I noted the population for sampling size of course. Seems like the 2.7 would offer 2 more MPG's over my 2010 F-150 with its 5.4 liter motor (and the 2.7 certainly delivers more oomph and torque all over the powerband.