I had a new set of tires put on today. When the tech turned the right rear tire, there was a bit of a wobble. He pulled the tire off and checked the balance again, and that was fine. He also turned the hub that the wheel fits on and there was a wobble on that.
He told me that he thought that the axle may be slightly bent.
If it is bent outside the bearing area or at the hub, you can stretch it out for a while, but it will cause some funky tire wear. We had one bent on an old 74 powerwagon and drove it that way for years, before replacing the axle. It may also cause some bearing wear, but usually only if it is bent in that area of the bearing or inside the axle shaft housing.
I have a 96 b2500 with the exact same problem. right rear vibration starting at 40 mph , as if you were under a bridge with a run-away freight train overhead, and eventually smoothing out at 70-75 mph. After being stone-walled by the [email protected]#$%^&*() dealer 6 times from whom I bought it, I finally said [email protected]# %^, and went through the most simple obvious items first,i.e. tread,balancing, and finally, jacking up the back end, putting it in gear and watch that wheel spin like a paint shaker. That infamous day was March of 2003. I am still driving it. I'm debating whether to go to a boneyard and swap it out, rebuild it, or go to a merciless, motherless, satan's-pride-and-joy,[email protected]#%%&*()+ dealer and "RAM" it right back up his merciless, motherless, coldblooded,satan's-pride-and-joy,where the sun don't shine,looks-just-like-a-salesman's lips, [email protected]#. By the way,it was a ford dealer.