had a few 3.8 cars and just got a 3.4 nox with bad headgaskets and upper knock? its an 06 so it has roller lifters and rockers. cleaned all lifters and all depress properly. inspected all rockers. motor runs cool now but still has knock. so, i have clean lifters, rockers, good pushrods, valve springs all look good. i removed valve covers and all rockers/rods seem ok. all are tight and i can turn/rotate pushrods at tdc. so, whats next? worn piston pins?