I'd bet that the wire or the plug is shot. Since #6 wire can lay on the O2 sensor or manifold back there, it's possible it just melted the wire and is arching. Worst case, swap the coil w/ another and see if the miss follows since all the coils are the same. If it stays on #6 then you know where to look.
The P0420 is due to the high flowing cat.
P1811- Did you ever notice your car slamming into gears, even under light throttle? This is usually caused by a failing PCS solenoid. A trans fluid and filter change, a bottle of lucas stop-slip and a shift kit should help eliminate this.
P0128 could either be a faulty thermostat, or a bad Engine Temp. Sensor, which this is located under the thermo. neck in the LIM, kinda at an angle.
