It got plenty of LS additive and synthetic oil.

I will try to dismantle it as much as I can tomorrow, but will leave the diff cover in place so I can actually get to work for now. I will pull driveshaft first and check there, then head to wheels/brakes/seals. The amount of backlash alone makes me lean away from axle bearings. I can "rock" the truck going down the road and do not notice a change in pitch. Only throttle input changes the sound.