Suburban Issue

99 Suburban, 350. 4wd, posi rear, 162k miles. started making a weird rat tat tat tat tat tat noice when slowing down below 35 mph.
Oh my god I thought it was going to cast it's withers. Pulled the rear wheels and drums, did the right side first because it sounded like that was the place where it came from. Trailing shoe friction surface was broken in 3 places and the drum was burned a deep mahagany color. wheel bearing seemed tight and quiet. Pulled the differential cover, no excessive slop in the pinion bearing from what I could see, Gear wear surfaces looked corre ct from what I can remember. No sharp edges, nice even pattern. Cleaned everything up and put it back together. Spent 2 hours on the drum with cordless drill, wire brush, sand paper. got it looking relatively normal. New shoes all around. I thought I was pooping in tall cotton until I jumped in with the truck on the jackstands, started it up and reved to 35 mph. Perhaps a tad less pronounced but the noice is still quite noticable. Any thoughts? Posi gone? Pinion bearing? Was on another forum and got a lectur for running the truck vor 5 seconds on the jackstands but no help.
Thanks much
Bill