I have an 06 2500hd crew cab. My truck has been throughing a code 455; large leak in evap system. The info center on the dash tells me to tighten fuel cap I had this problem back in the spring. Put a new cap on and I got the code once more after that then it stopped. Now for like the past month or so it has been doing it again. I wonder if it has something to do with the colder weather. I any case does anyone have any ideas on what it can be? Or where to start looking?