Well the in and out is not too much of a concern cuz there is play that direction but the back and forth your talking about is puzzeling.
Remember the outer splines on the hub itself? They ingage to the splines on the inside of the wheel hub/housing. So the only way you could have slop there is inbetween the splines??
I don't know man?
By some Warns and replace them
hahaha
Maybe pull um and put more greese in there..
Good Luck!
Burt