Torque was breaking them. Turbo 3.0 Supras spinning 9k rpm to make power don't make the torque of 7L turbo + nitrous V8s making the same power at 6k rpm. HP doesn't break drivetrain components, torque does. And more than anything, the shock of a dead hook high rpm launch does. There again, a big V8 has a lot more rotating mass. Also, I dunno if you're referring to magnums, but back in those days, this was before the 6060 or the magnum, and no stock T56 takes 1300 rwhp at any rpm for very long.
Anyways, those guys finally built what I did, the g-force geared t56 and it solved their problems. It has a reduced helix angle and 9310 alloy. Still the strongest H-pattern transmission I'm aware of, but the magnums are doing some amazing things.