I have a 2015 Ram 1500 ecodiesel with 34,000 miles. 1.55 gear ratio and full size topper. 90 percent of my driving is interstate and about 25 percent of that is pulling a 3,000 lb trailer. I have never once gotten over 21 mpg. Usually average 18 to 19 mpg with out trailer and 12 - 14 with...