Two thoughts here
Don't take offence, just spit balling
did a u-joint cap fall off during the gear replace and lost a needle or got a piece of trash in the cap?
or, did the slip yok, get remove and put back together out of faze. When you put the yok straight down, is the pinion yok straight down......or off a spline or two.......
This is kind of a cheese video, but if you fast forward to the 2:00 minute mark, it explains what i'm trying to say.