do you have it set to retard the timing when you start boosting.... if not you could be getting detonation which is hard on everything in the motor... also always always always check clearances.... so many factors... theres no perfect machining on anything, its close... really close but not perfect... then theres your torque wrench it could be a little off on torque.... and can get more and more off depending what depth socket and extension you're using....then there can be things such as bolt threads that can throw torque off.... that plastigauge stuff is one of the cheapest securities when building your motor...