Just curious, do you know how much torque an S5-42's seen and been demonstrated to accept long-term, beyond the factory ratings?
Never ran my 460 on a dyno but DesktopDyno says:
You must be registered for see images attach
I've broken I think three S5-42 transmissions. They tend to break when shock loading them like barking 38s too many times on the 2-3 and 3-4 shifts, suddenly catching while spinning off road, tugging stuck trucks out. Always case or mount failures and always seemed to coincide with shock loading. Never broke one driving normally, that is accelerating briskly and shifting at ~1800 RPM. FWIW the last one in that truck was still going strong after 2 years of use/abuse. Trans failures did seem to increase after upgrading to 1350 joints, though ujoint failures sharply dropped off. I think the key is don't shock load them if you got an engine that makes torque.