Jim, thanks for the travelog and equipment comparo. Recently i had to deal with a gearing change and further had to mitigate the weight vs. power/torque vs. gearing equation. Coming from 3.54:1 pigs, and adding 35" tires and heavier wheels to the mix, I had to explore optional gearing for my GEN II RAM, 2-series truck with an NV5600, 6 speed manual with a 27% overdrive. This led me to this fun page: http://www.grimmjeeper.com is the best gear ratio calculator on the net, and I used it to develop a regearing strategy.
My two choices for a front Dana 60, and a rear Dana 80 were
4.10:1, and 4.30:1, both of which would fit my cases. I chose the 4.10's because of the lower torque max of the Cummins (which runs best between 1700 and 2000 rpm, and that they are stronger than the 4:30's), vs. the higher rpm comfort of the Navistar V-8's.
Ford certainly did their homework when developing gearing that would work in the specified power bands in their trucks for the most users.
jefe
