Bring your drive shaft to a shop that balances. They normally will check it out free.
I read that the vibration can be checked with a container of water placed on the floor board then drive it at the speed the vibration starts. If the water ripples it's the drive line. If it splashes around, its the tires/rims/bearings?
On the wifes '70 Chevelle, I had an annoying vibration. I replaced the front end with an alignment, all four wheel bearings and even the complete rear end. I had the driveshaft and all four wheels balanced.. still had the vibration. Rechecked everything and had the wheels checked again but this time I watched COSTCO balance it. I noticed that one wheel wobbled and asked if the car would vibrate with that wobble. The tech didn't know, he said that he just puts the weights on where the machine indicates. I then replaced that rim and guess what....vibration is gone
.
Upside is that my drive line are all new
.
