On a brand-specific forum, one single owner had a vibration that after many visits to tire shops, suspension shops, and dealer shops, it turned out to be an out-of-balance 2-piece drive shaft. The original Ford shaft was replaced with a longer one to accommodate a stretched frame for a longer wheel base. Taking the shafts in for balancing didn't solve the problem. They had to get balanced together on the vehicle. It got complicated but finally did get resolved.
Just keep that in-mind as you march down your own road to resolve.