I run a 95 diesel dually 2 W/D with a 6 speed stick and with my 43' trailer I get 18 mpg once I hit the Expressway... city traffic and lights kills my mileage... my trailer has a real small front to it(custom) so I'm not dragging a wall behind me... also I try to keep my revs at 2000 to 2200 which is 65 mph or a bit higher... it has the 4.10 gear but I did put the tallest tire on it that would fit