I don't think its the transmission. I had the exact same problem, replaced the plugs and it went away. Always start at the plugs! One fowled plug and I thought the transmission was gonna fall out! With the engine running in gear on lake at idle, unscrew each coil pack and lift them off the plugs one at a time, when there is no difference in idle, you have found the culprit. Replace that plug and your done! Or...skip the whole experiment and just replace them all, knock gone and enjoy the day! Keep us posted!