Originally Posted by SandyHook
In conversations like this I always like to point out that Ms Hook and I get over 13 MPG when pulling our 12,000 lb 5th wheel.
On flat ground near sea level (I-5 in California) we generally run closer to 15 MPG.
That's impressive. Is the tow vehicle a diesel? The OP's mileage sounds about right to me. We pull a 5th-wheel+boat combo that weighs a little less than your fiver. I've yet to get 7 mpg. Usually 6-6.5. I suspect that some of the difference is due to friction of having 12-wheels in the ground, and that our rig as a whole is very un-aerodynamic (gaps betweeen truck/trailer, and trailer/boat). We've just had to accustom ourselves to the fact that a long weekend at a faraway lake will usually run us around 120 gallons of gas, when truck, boat and generator are all fed. But having the place to ourselves is worth it.
On edit: The truck is a gasser.