[baldlobo]

first off the tj's are an areodynamic disaster; if you have any lift, probably won't help matters.

1) definately not worth the 3-400 considering you'd probably get less than 1mpg from said mod.

2) is it an lt or a p tire; lt's weight more than p's

3) don't think it matters much on the 4.0

4) warm air is better for fuel economy; that said most "cold air" intakes aren't cold

5) there are two ways to accomplish timing advance one is cam which should increase torque and then the other is ignition advance which should bring up efficency

Other then that; i think alot can be done to the front of the tj's to improve mpg

1) cover the front diff + an inch or two

2) cover the front wheel wells

3) block in the tires(cover in most of the wheel well's)

4) minimize the dead zone on the hood(it's huge)

5) try to reduce the rear wake (via kammback/gas tank mods(ala gc gas tank slope)

ps. my best tank was 400km/55l or 13.75l/100km; average tank 340km/55l=16.17l/100km