I guess they were designed in the days of 20 cents a gallon for gas and no highways but I do want to see if I can get the mileage back up some,I am going to step the gears back up to around 3.50 and I forgot I drilled the main jet in the carb a little so I will install the jet from a parts carb and see what happens. With the 4.10s and the fenton headers it was running a little lean so I drilled the jet out a little but with the talller gears now it might need the smaller jet back in,when I put the T-5 and modern rear end in I was not expecting any more gas mileage but the drop in mileage suprised me.