The stick set up should give you the best mileage but the O.D. gear may not be needed much with the driving your planning on doing with the lack of power in direct gear and worse in O.D. If you're after a lot better mileage I would look at a CTD 12 valve conversion with a manual tranny with O.D.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)