I'm not sure you are going to be happy with the improvement overall. The 4 cyl will be working a lot more and the truck will feel that much heavier, probably without gaining that much in mileage. If you want to improve mileage think seriously about getting rid of the 3 speed. a 4 speed auto with overdrive or better yet a manual with over drive will make all the difference. Same driving experience, but better mileage.
