I'm back... I forgot my phone when I headed out yesterday, and was almost to Ft. Walton when I realized it. Hit me again when you have a second, I'll be at the house all day today...I think.
I suspect the job of balancing was less than stellar, as evidenced by the improvement you noticed after a rebalance. I kinda think you may have a worn output bearing, as hubs have to be pretty loose to cause vibration; I am pretty sure you'd hear it before you felt it. Could be a CV, despite being new, but a source of trouble on 60/65Es has always been the output bearings. The better news? You get to split the case to replace 'em. Now if we're talking differential output bearings, that's a little better news... When you say you noticed the shaft had a little play, what shaft are you speaing of exactly? Lemme dig up a diagram...
...or 5. See anything that looks like what you're talking about?