STRANGE axel twisted?

Buddy of mine did the same thing last summer with his 550 HP 408 in a 4 speed duster. Replaced the axle just to snap the next one. 3rd time around he broke the pinion rite off the rearend. Alot of wasted money later he is swaping to a Dana 60. To much tourque and slamming of the gears for the 8 3/4.