Have you checked the spark plugs?
Another thing you could check are your ignition coils. Sometimes for good troubleshooting measure, you can move one coil to a different plug to see if that cylinder begins to misfire. That way, you know it's the coil. If the same cylinder is still misfiring, it could be your plug.
you can get a new ignition coil
Here
You can get the plugs from AutoZone, CSK Auto, or really any auto parts place. Make sure to get the NGK Laser Iridium plugs.
Anyway, that's all I have for my 2 cents. Good luck!
EDIT: It looks like that link doesn't provide the ability to buy the entire coil itself. Go back and choose 2004 as your model year, and it should give you the choice to buy the entire coil assembly. I believe they run at $75.