2004 Dodge Intrepid Random Engine Misfire Dodge Intrepid

Hello. I have a 2004 Dodge Intrepid 2.7L V6 with 99800 mils. I was experiencing bad fuel economy and replaced the O2 sensors, Plugs, and Coils. After this I was experiencing a Check Engine light and rough engine performance when accellerating. At first I did the front O2 sensors and then realizied I needed to do the rear ones. After that the car still runs rough. My mechanic did a diagnosis and told me to have the ECM flashed and it should fix the problem. I did that and $100.00 later and 6 weeks, my car is still running rough. Dodge told me that I was having a code for a emissions leak and the upstream O2 sensor was reading high and they needed to diagnosis it again. I am about to take it back to Dodge but am unsure if this is covered by my extended warranty. Could I just have one Sensor that is bad and just needs to be replaced?

Any ideas would be appreciated. Thanks