I have a 2009 2500HD 6.0. It is running rich in both banks. It is non flex fuel with black gas cap. I have owned it since December so about 10 months and codes will not go away. Only 2 codes I have. It runs good and idles ok just uses a lot of fuel. Plugs are slightly black. I have changed knock sensors 02 sensors and maf sensor with no change. What else can I do?