It's probably just one of those "who knows" things as to why it broke. I got the transmission put back together yesterday and today I got the truck put back together again and so far so good after about 35 miles of driving. My transmission is now equipped with the factory steel/iron four gear overdrive planetary, the shorter input shaft, a roller center support and a six gear forward planetary so I should be good to go. This engine made 330 horsepower and 510lbs/ft torque when I ran it on the dyno so nothing too powerful but it really does run well and this trans works great hopefully it'll keep working now!
Any sufficiently advanced technology is indistinguishable from magic --Arthur C. Clarke