Shimmy/wobble in rear

[Houston Ben]

Hey all, I have an 86 c10 with a 85 rear end and have a shimmy/wobble in the rear. I jacked up the rear and ran it (didn't video that part ) and the wheels wobbled pretty bad. they weren't moving in and out, but like they were out of balance. I had them balanced this past Saturday but no luck. at least one of the tires took 15oz to balance which probably aint that good. In the vid's posted you can see I can move the axle in and out approx 1/8 - 1/4 inch and if I go side to side or up and down they move a little. Also, the drive shaft is smooth as butter. I have not replaced the axle bearings, they are the same as when I bought it. The wobble/shimmy shows up between 40-50 mph and gets worse the faster I go. I can drive it but it is really annoying!!

Can anyone help this poor soul?

https://www.youtube.com/watch?v=VW_Z...ature=youtu.be

https://www.youtube.com/watch?v=a0n5...ature=youtu.be