I get 10-12 around town and 14-16 on the interstate, depending on how I use the throttle.

 

imagine what u would of gotten if u did the speed limit around 65mph.
For every 5 mph you reduce highway speed, you can reduce fuel consumption by 7%.

so maybe you would of gotten closer to 20 mpg

 

My experience on a round trip to Austin Texas this last weekend (6 tankfulls, and 1800 miles) that in areas where I was running 60-65mph I actually got slightly worse mileage than when I said screw it and ran 75-80mph. Every tankfull (hand calculated) I got 13.3 to 13.6 mpg. I-10 is pretty flat except some small rolling hills in texas and florida. I know theoretically you should improve mileage going slower, but I found at 65-70 mph there was alot of shifting going on going up small hills,where as at 75-80 the truck would just pull the hill in OD.