i agree about the 3.9 being a poor choice. they have 4cyl. power with v8 gas mileage. i have an 03 dakota 4x4 w/3.9, 5 speed and 355 gears. it averages 18.5mpg(it increased by 1mpg w/k&n air filter-really!) when i`m trying to get the best mpg i can out of it. build a 318 with a small cam, small carb and good exhaust and you will get better mpg with more hp and torque than 3.9