changing jeep motor

not without changing a slew of other components. It's a jeep and they are not known for being gas savers. Put a cold air intake on it, change fuel filter, make sure spark plugs are good, and remove anything heavy from the car you down need. More weight=more engine pushes to move the car=less gas. You can also put small wheels on it, rotational gravity saves a nice chunk of gas when you have lightweight wheels. All this you may get around 3mpg more base on how you drive. If you need a true gas saver, trade it for a Honda or Toyota, both consume less gas than your jeep.