I recently had a misfire and knock in the bottom end of my 2000 gtp, i replaced it with a 95,000 mile engine from junkyard that is stock with no mods, sounds great but still has a misfire on the same cylinder as the other did, drive it easy and stay out of boost and under half throttle its smooth with no misfires on scanner, and this is with the sensors, coils and everything that came on the jy engine, i have swapped coils, 3 different icms, swapped injectors from known good cylinder, plugs, wires, miss will not move, even tried smaller gap on that one plug and it did not help, plugs are ac delco iridium 41-101, no light on and no codes, car runs perfect with sc belt off, what do i do next? Pcm problem?