Rear Pinion Clunk with Suspension Travel

Hey all, I searched around and didn't find anything exactly like this. I recently did an AAL (gained about 4") and U bolt flip, since then I noticed a clunking sound when going over rough terrain. I'm able to recreate this noise by standing on the rear bumper and bouncing the rear suspension. I have to bounce as hard as possible to make the clunk. The parking brake was one and the noise is present in gear or neutral. Manual trans.

Upon testing around with a stethoscope while someone else did the bouncing it seems like the culprit is the gear lash in the rear pinion. When I hold the probe on the center of the rear end housing I hear the noise the loudest through the earpiece. I can rotate the drive shaft a few degrees (maybe 1/8") back and forth while the wheels are locked with the parking brake, and I can see it rotate slightly with suspension bouncing.

I know some lash is normal and required for proper operation but any idea why I've not heard this noise til my AAL and U bolt flip? U bolts were checked and re-torqued to 90 ft-lbs. I'm taking a trip in a few days and I want the truck to be safe and reliable.