Weight is a factor also. Differant types of tires + air pres. can make a differance,correct whl alignment, brks not dragging, dirty air filter etc etc have an affect on fuel mileage. Having NO CODES helps too Guy.
In a car like yours a 2.2 may be a bit under power when it come to acceleration. Torque convertor NOT locking up on the hightway will kill gas mileage too. ( code 37 ) Guys having been playing with custom calibrations for more performance and upping the fuel mileage too. Manual transmissions, tire size, FD ratios all have an effect. Food for thought, the 2.5 has more torque than the 2.2 but won't rev as fast or as high. But it has the power to turn a shorter gear which = better mileage. Torque moves mass, horse power keeps it moving. Now I'm sure you're really confused
Mopar or No car. Tires and Tits, Rock on.