I have a very similar experience. My Wife drives a 2002 Chrysler Voyager
3.3 and local driving never attains better than 15MPG. On the highway I am doing much better with a MPG of about 23. I have had the vehicle to the Dealer 3 times and each time I list fuel economy as an issue and they have yet to find anything wrong. Other than this I am very happy with the vehicle.Additionally I drive a 2004 Chrysler PtCruiser, non-turbo automatic and I get a solid 21 MPG local since new.