My 2000 tundra 4.7l v8 with 223000 on it is misfiring. This truck has always ran like a champ. But it started running rough the other day and the check enginelight started flashing. I checked the codes and po308 came up. So I changed all the plugs and the coil pack at number 8 cylinder and there is no change. One minute it's smooth and the next minute running rough again. Any ideas?