ok so I've had my car for 2 years it's awesome!! I travel to Washington from California. Its like 900 miles one way. So good on gas its not even funny. I've had NO REAL ISSUE UNTIL recently. It has been shaking when I'm at a stop sign or going below 40. I take the highway at 65 no problems. I had a diagnostic test nd it says it's MISFIRING. The engine light is on but I know the o2 censor needs to be replaced. I'm also being told that it can be the spark plugs/wires. Can someone give me GOOD PRO ADVICE. I don't have no money to really buy random parts.

 

Plugs and/or plug wires are the most likely culprit, especially if they are old or Bosch plugs. However, misfires don't always show up on a scan tool. I had a vibration in my '03 SS that bugged the heck out of me. Misfire nor any other DTC did not show up on a Tech 2 scan tool. Car seemed to have plenty of power. Decided to replace the plugs and wires for general maintenance and problem was solved.
Found Bosch plugs were installed by the previous owner and one of the wires was broken. The plug on that wire was sludged up from not firing.
It is also possible the ignition control module is bad, but it's expensive, so it would be worth trying the plugs and wires first. They probably are due anyway.
I suggest replacing the plugs with ACDelco Irridium, or NGK platinum ones with ACDelco wires.

Hope this helps.
Please post back with the results.