RPM at 70MPH

Put some taller rear tires on to knock down your rpm a bit if you want. Anything under 3000 is doable, just depends on how far you want to drive it. I am putting a 28" tire on a Duster with 3.55's and a 2000-2200 converter, hoping it stays under 2500 at 65 - no hemi. Should be a good cruiser, sounds like you are about right, keeping the rpms in that 1700-2200 cruising range @ 60-65 is kind of the ideal.