2006 LBZ, Allison Crew Cab 3500 Dually, 4:10 gears 4x4-all stock. Wifes truck, pulls a 14k 5th wheel horse trailer EXTREMELY WELL- no complaints there. Mileage seems low, especially when empty. 8-11 mpg when towning ( I'm thinking not bad, most in hilly PA.) Empty is 12.7 average rural and...