one piece driveshaft vibration 60+ mph horrible

[gotboost1099]

so i got my driveshaft from z1 they sent me a 2+2 shaft and it needed to be shortened or my tt convert. i was past my 15 day return. so anway i had it professionaly shortened and its fine up till 45. 50 to 60 vibrates but not horrible than 65 and over it vibrates so bad it sounds like im hitting rumble strips on side of highway. any ideas?

[Z-owned]

since you had it shortened that could introduce issues with it not balancing out properly, but assuming everything is balanced, try unduing it where it meets the diff. and rotate it 90 degrees.

[adubon]

it may not be balanced.