A855 - 5 Speed

think it can be summed up in
torque handling or torque capacity and shock load handling or capacity are two very different things.
A shock load Tends...Notice i say tends...... towards infinite for an infinietesimal moment in time. and any mechanical system can only recover from that a set number of times you can't measure it easily so you cant supply a rateing.

if the wheels don't move and you unleash the full torque of the motor on the unsuspecting drive train once twice thrice ..... you will break the box or diff eventually. evety shock load alters the bonding and grain boundaries in the structure of the shocked componets. work hardening brittleness, loss of elacticty and the number stress risers change in form and value.
hence you could in theory ruin a hemi spec A 833 with a slant 6.

In the same way you can break a toughend glass screen with enough tap tap tapping from a pointed steel mallet. punching it, kicking it doesn't work, leaning agints it doesn't work... but the tiny plastic mallet with the steel point does.

torque rateing is "leaning againts it" shock loading is your little "plastic n steel" mallet.

Dave