I drove an old international emeryville for awhile that was a 5 x3.. a 3 speed rear end. Havent heard anyone mention that yet?
A 3 speed rearend is a tandem axle with two two speed rear ends. Low is both axles in low. 2nd is one in low the other in hi, and the powerdivider equaling them. and 3rd is both rear ends in hi.. worked pretty good...

What it will say on my Tombstone: "Boy, that guy sure owed alotta people Money"