I have a 2002 edge 4x4 4.0 and am getting horrible gas mileage .i have changed plugs and wires, oil change, air filter, occur valve, some vacuum lines and still get horrible gas mileage. What should I be getting out of a tank of gas I have owned a lot of rangers this is my first 4.0 are they really bad on gas or is it just mine any help on what to check next