I know there's probably about a 1% chance of this being your vibration problem, but my neighbor had a 70 Cuda, mainly a track car, 12s. He mentioned to me after a night at the strip that he started getting a vibration on the top end on his last two passes. A few weeks later late on a weekend night he says lets go make a few blasts so you can see what it feels like. Needless to say about 1/2 way through high gear it was so bad it scared the poop out of me. Then he says let me give one more try and i told him go ahead but i wont be in it.
Turns out he had cracked the pinion gear shaft/cluster in his sure grip.