I actually have my father's 2016 diesel this weekend with a 5k TC on the back while I'm use to driving a 2015 6.4 Hemi with a 2.5k TC on the back, both with the same 3.73 rear end. He gets 10.5-11 mpg while I get 11.5-12.5 mpg driving at the same speed. I'm not really impressed with his acceleration, nor with the noise. Do like the exhaust brake though. So I'm getting 10% better fuel mileage and right now diesel is a 25-40% premium where I mostly drive.
Something must be very wrong with that 2016 diesel. As with all my vehicles, I keep a log book in each and then enter the data into an Excel spreadsheet. I don't pay attention to the mileage displayed by the vehicle computer. The setup you see in my signature below consistently gets 13-14 mpg; empty it gets 18 mpg. I have never gotten less than 11 mpg, even towing when the truck and trailer grossed over 27,000 lbs. It is a manual tranny though, and has free-wheeling hubs installed, all of which help mileage.
