Brakes and rear axle for 800 Alex

Hello all. Normally I would get lost and off track looking for answers. Eventually finding them after hours of reading thread after thread. And I must say, a great many knowledgeable bunch of people we got here.
So for the last week while out and about in my 95 Chevy 1500, 2wd I would put it in reverse (auto) and all of a sudden it would lock up. The first thing I thought was I hit something. Put it in park, back to reverse and it was good to go. Only does it after it has warmed up. Did it again today. This time I left it in reverse, gave her some gas and it would do a burn out with my rear passenger wheel but the rear drive would be locked up. At first I was thinking tranny issues, now definitely leaning towards rear diff issues. Sucked out all of the gear oil and looked really good considering I changed it out 2 yrs ago. A little thin but not burnt or any metal shavings. Any thoughts on why it's doing this would be much appreciated.

The ring gear has to be turning for any wheel to spin, and to get one-wheel-peel, you have a singular axle not turning. I would suspect a brake issue instead of a drivetrain issue. The parking brake typically isn't strong enough, but I'd check it anyways. Pull the drum off and inspect the brake.

Thanks for responding. So the other day before I checked the rear diff I pulled the drum off. It took a rubber mallet and backing off the self adjuster to get the drum off. No scoring on the shoes or the drum. I expected there to be some with the almost constant squealing. Lots of brake dust (more than the typical Ford). The wheel cylinder visually looks to be ok. Haven't tried driving it in a few days do to stay at home orders.