Why is my 2008 Dodge Charger trying to idle down and quit?

About a year ago, my check engine light came on.  I started noticing this everytime I bought gas.  I started checking the gas cap to make sure the Gas Attendant was putting it back on tightly.  In most cases, it would be loose so I would tighten it and the Engine light would go off.  This happened on and off over a course of several months.  Then I started noticing that when I would be stopped at a red light or stop sign, while having my foot on the brake, my car would try to lurch forward and then idle down a little.  This went on for about three or four months but not everyday.  Maybe once or twice every two or three weeks. The problem has gotten progressively worse with the car trying to idle down like it is going to stall out.  The car actually shakes as well.   I took it the dealership but they told me they were unsure so they would have to keep my car for a few days and  start with pullling out the wiring  to check for shorts . I can't afford that so I took it to Advanced Auto and had them put it on there computer and it was showing up random misfiring so I had the spark plugs changed. This has not helped. I took it back to Advanced Auto and they put it back on the computer and it was showing that the four O2 sensors needed to be replaced.  I had those replaced today and the car is still idling and shaking when it comes to a stop.  I am not sure where to go from here.  Any information would be greatly appreciated.