8-3/4 Pinion Nut Torque???

You have got to be sure which diff you got.
If it DOES not have a crush sleeve, and uses shims, it would not be unusual to see a shimmed pinion run in with an impact, then some may do a final torque.
If it DOES have a crush sleeve, that could be started with impact, then final tighten with torque wrench.
The original shop may not have been incorrect dependant on the diff.
You may just have a bad bearing all along