[mels80ga]

I will start at the beginning of the problem so you will have all the info I have. At the end of the 2010 season my rearend let go. It came loose at the end of an 1/8th mile run at 95 MPH. During the winter, and for the most part of early 2011, I was buying parts for a 9" Ford rear. After putting the new rear in the car I found I also had a transmission problem. When the rear broke it took out the trans also. The output shaft was snapped into right behind the splines on the front of the shaft. I took the output shaft from another trans I had and went ahead and overhauled the trans, it had about 1200 passes and 5000 miles or so on it. When I finally got the car to the track I was having an issue with the flexplate hitting the starter under power, and there was a bad vibration in high gear right about the speed trap at the end of the run. No vibration any other time at all, and as soon as I lifted my foot off the pedal it would stop vibrating. I only made 3 or 4 passes and took it home. I spent 2012 in Germany so I didn't get to fool with it till this spring. When I pulled the trans out I found two cracks in the flexplate out near the starter ring. I thought I had found the problem. Well a new flexplate cured the issue of hitting the starter, but first time out this year the vibration is still there. This is with two different converters also. The only time the vibration is present is in high gear at 90+mph and 5000+rpm. With the Ford rear I only have about 1/2 inch of play from the end of the u joint cap to where it seats in the pinion yoke. Could this cause that by the driveshaft bottoming out on the output shaft? Or would you think there is another internal issue with the transmission? It was very violent when that rear broke. Sorry for such a long post, I just wanted to give all the info I could.