Yeah this is what I think too and there is STILL slop in the caps even with the replacement u-joint...
So going back to my original question that no one's really answered yet... How often do rear pinion yokes fall out of spec? The only explanation I have for the slop in the new u-joint caps is that the rear pinion yoke has "spread out", meaning, the dimension of the two locations (where the rear pinion yoke interfaces to the two arms of the u-joint) has somehow increased, leading to the slop.