Just dropped trailer off for a few weeks in the North. 31 ft. Pilgrim - 11,000lb loaded. Avg. 11-12 MPG driving as slow as 55MPH, and as fast as 75 MPH (10 - 11 MPG). Wind condition and the frontal area of your trailer (yours sits even higher than mine as a 5th wheel) creates a huge drag. No shortage of power. Mine is a one (1) ton, and I recommend it with the load you're moving; you'll forget it's back there literally. One the way home, unloaded, she averaged 19.2 MPG running 60 MPH on cruise. Dropped to 17.5 MPG at 75 MPH. Truck currently has 10,500 miles. Numbers don't seem much different than yours. Hope this helps.