My guess is you have a V6 with AT, 31" optional AT tires, ADD and a roof rack. The EPA estimate (over stated) was only 14-18 MPG when it was new. That transmission and engine were noted for lackluster performansance - so year 10 could be expected. None of the other Yota engines is near a drop on replacement. GM 3.8 is good engine - and is frequently used to rplace the stock one for better performance and better gas mileage..