I had the original 3.42 gears that came with the truck replaced with 4.10 gears. I also removed the factory locking rear differential and had it replaced with an Eaton Posi limited-slip differential. The factory locker could not handle the amount of torque produced by the new engine. I bought all the parts from a place called Power Train Truck and Auto parts. They had resonable prices and great service. I reccomend them highly. Here are some pictures of the gears and posi: