I know you pulled your hair out struggling with this. So just to rub it in listen to a weird one. I was changing out the 7.5 non-posi carrier for a GM 7.5 guv lock part time posi in my old Malibu wagon.The 3:23 gears and bearings were staying the same and I was not even touching the pinion at all. I was prepared to re-shim the carrier from scratch since that is the normal drill. As I eyeballed it, I noticed something strange about the fit. I took the cast factory shims and merely reversed them from side to side. It looked good. I checked the backlash, pre-load, and contact pattern and they were all perfect. HOLY COW! That NEVER happens. So know that every time you touch the rear gears it is a different experience. Some are easy, some difficult.
