The alloy diff cups won't actually prevent the pinion gear from stripping. Correct shimming of the diff case or an alloy diff case also correctly shimmed will go a long way to preventing pinion teeth stripping. The cheapest way also is not to be so heavy on braking, because as the brakes are locked on stopping the pinion gear from turning, there is usually still enough inertia in the wheels to keep the diff turning thus breaking teeth on the pinion gear.