First, let me say that the car in question would be better suited with a dana.
I don't agree with the forensic explanation by Monte though, and here's why.
I was breaking ringgear side caps on mine(3 times), and also seeing chipped teeth. Had I stopped there, I would have agreed with Monte's explanation.
I went with a heavily gusseted housing, and added cap support load bolts. Still using the factory caps. I no longer broke caps, or chipped teeth. The failure at that point was pinion shaft shear. After 2 episodes of that, I went with a strange ultra case 9 with 35 spline pinion. Never even had to think about the rear end again.
8 3/4 has its place. But it's not under the car in question.