The guy who told you to use a different rearend gear is right.When it comes to fuel mileage,gearing is the most important thing involved.So you either go to a higher gear ratio or an overdrive trans,to keep the engine RPMS down at cruising speed.If you are just using it for transportation a 3:08 rear or an overdrive transmission should do the trick.I am running a 350 Chev SB with a 700R4 trans.and 3:90 gears and getting 20 MPG.The 700R4 being an overdrive trans.which is turning the rearend at about .78 to 1 ratio.
