I could do that (Replace the engine with a 2.4 Litre model) but might wait, And end up with a 2002 2.4 Litre model instead; Those get higher FE than the 2000 models according to Automobile-Catalog.com:
2000 2.4 Litre (Average Range of 407 Miles estimate, 12 miles higher than the 3 Litre estimate - And I've seen 28.56 MPG or so on a 359ish mile tank)
2000 Dodge Caravan 2.4L fuel economy review (model for North America U.S.)
2002 2.4 Litre (Average range of 440 Miles estimate)
http://www.automobile-catalog.com/ec...n_ec_2_4l.html
I'm already capable of managing 24 MPG in the 2000 3-Litre; 26 is easy in a 2002 2.4 Litre with the ways and places I drive with what mods I have (Mostly without city/town miles lately.) Plus some mods and? I'm already sitting on 30.