When braking < 5mph; Rear differential Lock-up

I have a 95, manual, 4x4 with 250k miles.
I've encountered a new problem involving what feels like the Rear differential/axel locking up when i slow down < 10-5 mph. The rear end locks up entirely, i noticed a quick escape from the issue when it stranded me at a "Red" and couldn't afford to hold up traffic;
I threw it in reverse, rolled back about 1 inch to the sound of a loud metal "pop" or "thunk" and the tires released.

I also noticed that i could almost feel when it was going to happen because there was a little more pull on the truck when slowing down.

Any Ideas/fix suggestions?

 

Maybe the rear brakes sticking?

 

Best guess is that you have a leaking rear axle seal. 90 weight gets on the drums and acts like glue, especially where you live at this time of year. Crawl under and look for signs.

 

I'm having a similar problem. It feels like the brakes grabbing. It only happens when I'm barely creeping along, like going thru a 'drive thru' fast food lane.

I'm pretty sure its not axle-wrap, since I'm barely moving, and there shouldn't be much torque on the rear housing. And I believe that would feel different.

I felt sure it was sticking calipers, so my first attempt to correct it was replacing the calipers... no change.
Lubed the rear drive shaft zerks ... no change
Lubed the rear drive shaft splines ... no change

Now, I think its the rear brakes.
I've adjusted the rear brakes ... no change
I've adjusted the parking brakes ... no change
I've inspected the shoes, and it all looks good, no leaking, nothing obvious.

Next step is to replace the rear brake cylinders.