R/R Tire locks up............

Could someone please help, I have a '94 Chevy 4X4 and it developed a small problem that has me baffled. I'm plowing snow.....when I back up, the right rear tire locks up, I'll move foreward, then back up again, sometimes it locks right away, other times it won't. Anyone ever hear of this?
I've replaced the complete carrier in the rear end and the problem went away fer awhile, but now it's back.

How about a dragging brake or a broken spring on a shoe or wet shoes. Maybe a lot of debris from ice and snow.

nope, the brakes work fine........this locks solid........in 2 wheel drive or 4.....and will slide the tire as I continue to move so I assume it has somethin to do inside the rear end, but not sure what as I just redid the carrier with another [same gear ratio].........the part that has me baffled is that it only does it backin up