Get a vibration analysis app for your smart phone - I use a free one called VibrationAnalysis. Take a reading at actual 60MPH and another at a recorded actual speed where the vibration is worst.
Verify your tire size’s true rpm/mile rating. From there all it takes is math to determine what in the drivetrain is causing the worst vibration.https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4891490/1
Knowing what frequency you’re truly feeling will be helpful.
You’ll get something like this if it’s legit wheel and tire:
And this when fixed:
Note the y axis.
When you know the number of tire RPMs/mile, and are at 60MPH, so its one mile per minute, the math starts to get easy.
Since the diff ratio is known, if its that, it will be mathematically the harmonic that is the ratio multiplier of the tire RPM, or more specifically Hz (oscillations/sec).