You could also switch to an overdrive trans and run more gear like 4.10s. I built a 440 Duster and made the leap of installing an A-518 overdrive. Go to my picture gallery and see the work involved. I have 4.57 rear gears and with the .69 O/D ratio it makes the final drive 3.15. The car is an animal around town and drives very nice on the highway also. Check my videos on my YouTube channel Doosterfy.