[redmt]

Buzz the basic setup is already done. If you don't have to change anything except the seal, it's only a matter of getting the nut tight enough and the pre-load correct. It is possible to overtighten the nut. Somewhere around 250-275 the shims can start it crush and deform and somewhere upwards of 300 you will find out the integrity of the pinion. The ones that are a real PITA are the 9" Ford and similar that use a 1 time use crush sleeve. Tackle one of those and you find out what a 3' breaker bar is for. OH!! and NEVER use an impact wrench. never ever.
BTW, end play is far more critical than backlash. You want zero end play. If you turn the pinion by hand and can feel it but not see it, that's close enough. If you feel it AND see it, it's time to check the pattern and either move the carrier over or sink the pinion deeper depending on what the pattern looks like. This is where the rotational drag come into play. You can't actually measure an negative so the next best thing is the bearing resistance , rotational torque. You probably don't have a dial inch pounds torque wrench. Grab the pinion across the flange with your thumb and little finger. If you can turn the pinion , it's too loose. It should take a light to moderate amount of twist to rotate it.
I hope that all makes sense,,,,,