1) Where is the fuel filter on a '04 Ranger 4.0L?
2) What is the recommended mileage to change rear diff. limited slip oil?
What type of rear diff. oil should be used if the ford oil is not used with the additive for limited slip?

 

The fuel filter should be under the passengers compartment on the drivers side frame rail.

The rear should be good for 60-70k miles unless you get it under water. Non FX-II takes 80w-90 gear oil and 4oz of friction modifier, if you get it at the parts store just make sure it meets the Ford specificaton in your owners manual.