these are simple motors, ignition and fuel. coils break down under heavy load if there going bad but you changed them, maybe ground? same goes for fly wheel and stator. you changed carbs , but have they been gone through? new needles venturies ect? not questioning your skills but often small stuff get over looked. i have no experiance with the lock out clutches. but i do have alot of experiance with cvt clutchs on sleds. clutching plays a huge role on how a sled performs. sticky weights, sticky rollers, springs do wear over time and need to be replaced. if the lock out clutches have rollers and weight arms id check them for wear... if none of that helps check your boost bottle and swap green power band for the red or black one and drop fuel mix ratio to 200:1