Let me start by saying this site is great!!!

Now to my problem I have a 06 2500 extended cab 4x4 with a 6L and automatic trans. with 106,000 miles a few weeks ago a message came up saying check fuel cap did that and found no problems then today a check engine light came on I pulled the codes and came up with po449 and po455 from what I found the emission vent valve has failed some way and that the evap emission control system has a leak as well should I just start with the gas cap and work my way through all of the parts or is there a better way to pin piont the problem.

Thanks for any and all of your help Steve