Nasty vibration from rear of car

i'm having this problem that just started, about 2 weeks ago i had 3.73's put in and the left axel and bearing was also done, anyway when i hit about 100 km/h (60 mph) theres a nasty vibration from the rear end that i can feel in the stick, i thought maybe one of the weights on the drive shaft fell off so i raised the car put it in neutral and started spinning the tire to turn the shaft to see about the weights when i noticed that the driver side wheel, i can pull it about 1/16 - 1/8 towards me and back in, the passenger side is rock solid (no play), i didn't think this is normal but thought i'd post and see. I think here lies my vibration problem?!!?!?!?. i'm taking the car back to the shop tommorow and make him fix it.

Well i took it to the shop and the guy was like, "nah it has nothing to do with the axel" so he raises the car and pulls on the wheel, and it moves a bit back and forth, a funny look comes to his face, and within 5 mins that diff cover was off, and he was poking around in there. so i came back 2 1/2 hours later and he's just putting the finishing touches on, ha says he added some shims and some other stuff, so basically i got a complete rear tear down and rebuild for free , needless to say the vibration is gone now, except for a little bit from the drive shaft, which was always there, i think i'm gonna order a drive shaft from summit or jegs as long as not gonna get slaughtered with duty charges for bringing it over the border.