I continue to be amused by "Why is my mileage so crappy?" threads.

Reasons:

1. Driver. Swap trucks with your friend and he will get better mileage in your truck. Drive his truck, and your mileage will suck.

2. Ignorance. A lot of energy is expended by pushing air out of your truck's way. In fact, the coefficient of drag squares with doubling of speed. Just an extra 5 mph on the highway sucks a disproportionate amount of fuel. At 46 MPH on a empty two lane road, my truck got 24.8 MPG - that's hand calculated. Aerodynamic drag is MUCH lower than 65, the transmission is in 5th gear, and the engine's torque can move the truck at not much more than an up idle.

3. Compare apples to apples. I have a 2005 XL Regular Cab Powerstroke FX4. It weighs 7,280 lbs. with a Snug Top camper shell, grill guard, Hella 4000 lights and 3/4 of a tank of fuel. My friend has a 2006 XLT Crew Cab 4x4 that weighs over a thousand more pounds loaded with a bunch of stuff he should clean out of the truck. He drives with a lead foot and can easily average less than 10MPG city/highway. If the cops catch him, he could average 6 - 12 months in jail.

4 More ignorance. Terrain and wind makes a huge difference in mileage