It's been a while since I've set up a gear set but have done several in my time. Some thoughts: Aftermarket pinion gears are marked with their installed proper depth. (Distance from carrier bearing split to rear face of pinion gear.) The rear bearing is shimmed to achieve the proper depth. Tapered roller bearings are typically very close assemblies. One can save a lot of work by buying two then grinding the bore of one to be a slip fit on the pinion. This saves pressing the bearing on and off to establish pinion bearing shim thickness. Factory pinion gears are not marked and can be trying to set up.
Pinion bearing pre-load is very important. Too tight and and the front bearing will burn. Preload can be touchy to set. Once a crush sleeve is crushed too much, too much preload, they can't be reset. (I've "straightened out" a couple to reuse but don't recommended doing so.) A beam type inch lb torque wrench is required to properly set.
Always stone the mounting surface of the ring gear and carrier to ensure there are no nicks or burrs even with new gear sets. Always use new ring gear bolts, install them with red Loctite and properly torque. These bolts transmit all the torque.
Gear set up is pretty straightforward but one must understand the assembly and have the proper tools to do it right. In addition to the proper torque wrenches, a test dial indicator and 1" micrometer to measure shims is a must. Access to a hydraulic press for bearing installation is also a requirement.