[eschaider]

While this may be just a bearing selection issue, I don't believe that is the case, no pun intended. The two carriers in your Post #10 picture look dimensionally different. The ring gear flange looks to be about 0.100" or so different in location, carrier to carrier. Additionally, you already observed differences in the external bearing/bearing register locations, which prevent you from using shims to sideload the carrier properly.

As long as you have dimensionally different carriers, one will not fit properly in the space the other came out of. Your carriers need to be dimensionally identical. The fix is to get Auburn to exchange the carrier you currently have for the correct one you need to use.

Bitter medicine, I know, but the correct way home ...

Postscript:

The differential you should use that will make a noticeable difference in how the vehicle drives is a Torque Biasing differential that directs drive torque proportionally to the wheel with the better grip. Of the various providers offering this differential, WaveTrac (wavetrac.com) is the preeminent provider.