Misfire Code Help
 

My 09 Q7 V-6 is showing 2 codes, one for intermittent misfire, and the other shows misfire cylinder 6, so I pulled the old swap the coil packs trick. I swapped 5 to 6 and 6 to 5 and cleared the code. Car ran nice no miss, couple of days later, down on power, CEL comes back on and its showing # 6 misfire again? Any ideas, usually this rules out that #6 coil pack being good or bad. Could that plug be fouling ? Why then ould it run better when clearing the code ??