The stock exhausts are just SOOOO restrictive that cylinder temp build-up is too much for the engine to handle and pre-ignition is inevitable. Witness the glowing headers when the engine is left to idle for more than a few minutes. It is dangerously strangled in my view and it's a testament to the strength of the S&S that they haven't spat their conrods out the side of the castings before now... Any Stage X upgrade that removes those restrictions is a valid fix, and I for one would add a vote for the G56 exhausts as they remove all restrictions, yet have sufficient volume to silence effectively too.