Have you got the JBA UCA extension? I never ran one and had vibes underload even after i had driveshaft balanced and several sets of ujoints before that.
dropped it down when sold and no vibs at all.
I have the 4 Link. I think I have over-corrected the down angle. Have been doing research now and think I know enough to get it worked out. I don't know how folks did this before the internet. Not having this info at your fingertips would be a big bag of suck.