[adamfgarner]

for what it's worth....I have the sm420, Dana 4.10 gears and 265/75/16 tires on my 1500 series...my tach reads just at 2000 for 40 right under 2500 at 50 and close to 3000 at 60...there are several calculators available on-line though there will be discrepancies as your tires get smaller with use and are slightly different from maker to maker...I am doing my first mileage test with this drivetrain...will post the changes when I do the 3.54 swap....as for my research I have found that 3.54 is as low as the Dana 60 carrier will accommodate...the 3.31 gearing might be a Dana 44 or other model???