2000 Mercedes ML320: Has 82000, warranty still available on some things. Misfire Code is P0305 (Cylinder 5)

My SUV is shaking when I am at a stop light/sign, when I am in reverse, and when I am at 15,000 RPM's.

All other forums suck, so I am hoping that this one will have SOME responses!

Yes, I know that it COULD be the MAF andcleaning it had no impact.(but that would affect more than ONE cylinder, right?)
---> Plus when I unclipped the o2 Sensor I had a reaction, so I know it's not DONE!

I have replaced the plugs yesterday and today I replaced the wires for Cylinder 5. I fixed them with hope and was left with disappointment!

I need help with ANY advice, I am losing patience and I am doing my best to avoid going the dealership.

Thanks for taking the time,
Frustrated