I also had a vibration on the highway that was mis-diagnosed as bad drive axles and turned out to be a bad tire (DOH!).
Haha, I had the same thing happen. Replaced everything that would cause it, and would still get a vibration only between 60-70mph. I figured there was no way it was the tires since they only had 10k miles on them. I replaced the tires and the vibration was gone.