From talking with my mechanic and Tripoint, it is the fact that I was using a solid hub puck.
Here is a 6 puck:
<img src=http://www.clutchnet.com/image/6bKwik.gif>
Here is a sprung 6 puck:
<img src=http://www.clutchnet.com/image/6bEz.gif>
The sprung disc sort of absorbs some of the shock, so it is easier on the tranny. It also is made to slip a little for easier take off. The non sprung is not made to slip.
If it were a sprung puck it wouldn't break the tranny. Also I was getting very bad wheel hop, which probably didn't help the situation. I recommend the engine mounts.
The reason we went with the puck is that the street disc is not much better than stock. There is no doubt in my mind that the ACT pressure plate with the street disc will slip when launching, especially if you boost the car. A slipping clutch can really hurt you when launching.