Oil Levels

[AgTires4295]

Okay so not too much of a problem, but I drive my truck 1-2 times a week and do the ol' once-over before I crank her up (ie check oil, CAI, tire pressure, etc.). So I checked the oil which was half way into the cross-hatched area on the dipstick (which is where it's been for about a month since I've changed the oil last) and drove the entire day on Saturday which was about 300-350 miles of highway/mountains. Came out on Sunday and did my routine to find that the oil had come down about a quarter inch on the dipstick. What causes this??? No oil in the driveway and no plumes of blue smoke.

[AgTires4295]

Update: Drove the truck this morning for 20 miles or so. Came back and checked it this evening...oil is at the add line and I noticed slightly blue/white smoke after starting it up again and letting it run for about 5 minutes (just a little more than usual and would say that most would have not even noticed). Not a happy camper. By looking at other posts, am I correct in saying that i should change the fuel filter?

[jesilvas]

I don't see how the fuel filter change would help this.
It's using/leaking oil somewhere. Basically only explanation.

[AgTires4295]

Leaning more towards injector o-rings after talking to a friend and hitting other pages on the forum. Fuel filter could probably use a change too though.