My 2009 GMC would get about 14 mpg pulling the load behind the Duramax at those speeds and on that terrain. It is 4wd and is otherwise stock with about 90K on the odometer. I would suspect he likely got around what you did (11-12) for pulling that load given the light weight, age of the trucks, four wheel v. two wheel drive, and the aerodynamic advantage of your trailer v. his. There are variables however that may make a comparison difficult (I know you know this but for completeness). First, the weight difference of the trailer would have little to do with the towing economy in your case and would likely not favor a diesel engine unless it were significantly heavier. Your trailer is more narrow and likely significantly more aerodynamic because it appears to tuck behind the truck better. The wide, square stance of the utility trailer is much less aerodynamic therefore dropping economy. I assume your Ecoboost is stock, you did not mention if his Duramax is and also the mileage he may have on it. Also, the side by sides with light bars are not very aerodynamic which also would likely hurt his economy more than yours. I know it may sound silly, but when I pull my big utility trailer v. my more narrow one I can see as much as 2 mpg difference over the same route, unloaded. I also do not get as good of fuel economy pulling my Gator XUV when using the same trailer as a do pulling my TRACTOR with the ROPS down (even though the tractor weighs much more) because the Gator's roll cage and light bar catches air the whole time, as wind resistance is the main contributor to towing mileage so long as the weights of the trailers are reasonably close. Therefore, my opinion is that you likely got similar mileage with these loads due to in part the factors noted but that it may not necessarily imply an Ecoboost is as fuel efficient as a diesel. I know this was not your intent, but some posters may interpret it as such. I should also note your towing mileage is fairly consistent with that I have gotten using my father's Ecoboost, which is also two-wheel drive. You have a nice-looking truck.
John
