well, I was getting a bad vibration from about 4000 and up... i replaced the driveshaft and that took car of about 90% of the vibration, but i still had it at 5000 and up. so, i was driving at speed and put it in N (per reading on here) and slowly brought the revs up, and it vibrated then as well not near as bad, but it did. so, am I correct in saying that the flexplate is the culprit? or what?

 

Sounds like you have read a thread i posted. I dont know if my vibration is fixed yet. I am in the middle of swapping tranny's now. My flexplate has cracks at the bolt holes where the stall is attached. My original tranny was making a growing sound. So i hope after spending all this f-in money that it is fixed.

Tranny will be in next week hopefully i will let everyone know when i get it back together...

 

Like I told a couple other people here......check the output shaft on your trans.I had the same thing going on and narrowed it down to the last thing being the output shaft. I told my uncle(very good tranny builder) and he would have almost put money on that it wasn't bent. Guess what? You guessed it! Output was bent only 3000 out and it shook so bad I could hardly stand it!! Even in the neutral position. Traver

 

I have a similar vibration when I step on it. But only when accelerating fast, up until it up shifts, after that it stops, even if I'm still climbing through gears.
It's only felt through the floor of the car, no steering wheel vibration and not in nuetral. Any of this similiar to your problems?

 

it seems to be how mine is too, though... get this.... last night, I stepped on from 20 and climbed to 80 6400rpm shifts, it was smooth as can be. im like maybe the trq arm flexing sometimes and messes the pinion angle out of wack could be the cause?? what do you think? I now the stock trq arm doesnt like 1.58-1.59 60's all the time