Jim,
Your axle is fine, they are supposed to do that. It is part of the way non-posi differentials work. (Think about any time you got a vehicle stuck in mud or snow and watched just one wheel spin.) The reason for this is to allow one wheel to turn faster or slower than the other in turns, hence the name "differential." (The inside wheel travels a shorter distance than the outside wheel in a turn.) Also note that the grand majority of these years' 1/2 ton axles were 3.90:1 gearing.
Steve O
