seems that the question gets asked alot -- mine is a 2016 XD PR Cummins, completely bone stock. 26k miles on the clock. I use it for towing my enclosed race car trailer and also especially during the winter it's my daily driver (don't want to get salt and crud on my new CTR). this week was a totally average week for me; drove 348 miles and started with a full tank of fuel. I used 1oz of Hotshot Secrets EDT every fillup, and I typically fill up at the same station every time. I tend to drive about 5-10 mph over the speed limit, and accelerate 'normally' when I drive. no super hard drag race starts or anything like that. a typical week is about 10% city driving. 20-30% highway, and 60-70% back country roads driving. this fillup was typical mileage and the average was 16.9 mpg according to the computer. I hand calc'd it also and it was 16.81 mpg. my truck's computer is almost always within .2 or .3 of the actual hand calc'd. BTW when I'm towing my 9k lb enclosed car trailer (thats about 70-80% highway and 20-30% back roads) I typically get 11-12 mpg. but that's during the spring summer fall, and that always gives a little better mpg. my winter mpg (always 16-17 mpg just like this fill up) is always about 1-2 mpg worse than in the summer (17-18 mpg usually). for such a big heavy truck I think it does pretty well.