I suddenly seem to be burning more fuel in my F-150 4.6. What should I be checking?

Make sure you've got a current tune up (plugs, wire, oil, all filters, tire pressure, etc.). Make sure your timing is correct and there isn't any additional drag on your truck. The other possibility is your not burning it in the first place, but losing to evaporation or leaks. Gas and oil quality makes a difference too. All of this of course assuming that you're just not driving faster or are heavier on the throttle.