This past month has been rebuilding an axle for my C10. The old situation was pretty extreme. Factory 10 bolt open diff with 2.56:1 gears. Back in the day, I'm sure that did great on the highway. I have swapped in a 700r4 transission so now have an overdrive. Considering the factory tire size, diff ratio, OD ratio, lockup torque converter, and a 5000 rpm redline, this was setup to do 256MPH. Great for fuel mileage, less great for anything else.
I bought myself a 12bolt rear end and have spent the past month pulling it apart, cleaning it up, and rebuilding it. 3.73 gears, eaton truetrac carrier, all new bearings and seals, new drum brake guts, new shocks.
Yesterday I pulled the old axle out of my truck and got the 12bolt in place. Today I need to swap the u-joint in the driveshaft and bleed the brakes.