Been through this, it's 100% pinion angle, you need adjustable rear links.
I had my drive shaft completely rebuilt and balanced, didn't help.
Balanced my tires on Hunter road force machine, didn't help.
Finally replaced upper and lower rear control arms, adjustable on both. Lined up rear pinion angle with drive shaft to with 1 degrees. Now it can go up to 100 MPH and it's smooth as silk.
Search - Toyota Double Cardan Drive Shaft pinion angle
https://www.triketalk.com/forum/atta...1&d=1487805932