you need to determine why it is missfiring. it could be a bad plug, a bad coil, bad injector, vacuum leak or low compression. this is why you need a real diag to determine the failure and move forward from there.
If the compression is ok, in that cylinder and there are no injector codes or ignition system codes, I usually look at the ignition parts, if the wires and plugs look old, I start by doing a basic tune up which is to replace the plugs and wires with AC Delco parts. Cheap parts will just cause you more grief! Then I re-inspect how well the engine runs.
I have a 2003 Deville and got exact same code. I replaced the ignition coil bank (front coil pack). Under each are 4 short spark plaug wires. under which are the spark plugs. It may be a good time to replace them If It Is time. The rear bank is a bear to replace. The front bank where cylinder number 6 is located is easy. I used every method od diagnosing with OBDll diagnosis tools. I finally just took a leap of faith and I was right.