F-150: low gas mileage

I have a 2002 F-150 XLT, 7700, 5.4L, extended cab, short bed with 38K miles. I get an average of 13.9 miles/gallon in about all unloaded (no towing or hauling) conditions. that seems low compared to what other folks are telling me. Seems like on the highway it should be closer to 17 - 18mpg.
any ideas out there on what i can do - or is this normal for this size engine and the heavy-duty tow package?

Thanks,
John

any ideas out there on what i can do - or is this normal for this size engine and the heavy-duty tow package?

Thanks,
John

Sounds normal for the heavy-duty tow package. You are geared lower than the guys gettin 17 to 18.

Sounds about right to me.