With my 2001 quadcab, shortbox, 4x4, automatic, 3. 54 axle I regularly get unloaded highway mileage of 20-23 mpg with conservative driving. Now with a 22 ft travel trailer weighing about 5000 pounds loaded, I get slightly over 11 mpg... the same as I got with our former 27 ft single slide 5th wheel which was taller and which weighed 2500 pounds more loaded. Same driving styles in all three situations. Why don't I get better mpg with the travel trailer than I did with the 5er???