Vibration above 50mph that is not related alone to stopping and that is not specifically felt in the brake pedal when pressing it is nearly always due to a wheel balance issue.
I recommend taking your vehicle to a tire specialist, preferably where they are equipped with a Hunter Road Force 9700 balancing machine. This type of balancer goes above and beyond a typical wheel balancer to simulate pressure onto the tire while spinning it for balance. It may suggest that your tires may need to be re-indexed on the wheels (that is, deflated, and turned on the wheel to a more suitable location for better balance), or it may point out a wheel or tire flaw that may or may not clear up with balancing. I suspect that more than one - if not all of your tires could be at fault.
Rhythmic vibration at high speed alone is never caused by alignment, not likely to be caused by an axle shaft or hub bearing. Brakes/rotors/drums are only the culprit if the vibration is felt upon brake application.
Good luck!