I found this:
P0306= Cylinder # 6 misfire.
I had the same misfire codes along with a check engine light and engine stalls. I could never get it to the dealer with the check engine light on. They were no help. I stopped buying high grade fuels at low priced stations and the problem has not come back. In fact the last check engine light I had with misfire codes was cleared by high end mid grade fuel!