You will get better mileage after the truck gets more miles on it but like all of us, you always want better. The wind really does make a huge difference in MPG when pulling a sled trailer. I was really whining because I drove the gasser rather than the diesel but the new truck is so comfy.
During that 20 miles I had a good tailwind and the computer was showing almost 17mpg but as soon as the wind switched it went right back to 10mpg.
On the trip home I was always bucking a crosswind or a headwind other than about 20 miles of the trip. On the way out I got 16mpg and on the way home I got anywhere between 8.5 and 10 mpg. I just went to ND last weekend in my new 20 with a Hemi and picked up a new 18' inline aluminum trailer. If I go to 2050 RPM my mileage will fall off pretty good. I have a 1998 12 valve Cummins that gets 18mpg day in and day out if I keep the tach at about 1900 RPM. I have been driving diesels since 1996 and the secret is to find the sweet spot in the RPM range. The low end power is better and the mileage is considerably better.:face-icon-small-coo Seriously, as stated above, the mileage people get varies very significantly from truck to truck. What you need to do is get rid of the new Cummins and find an old 12 valve and run it.