I have a 2010 chevy impala. The check engine light has been on for about a year. The codes are p0442 and p0455. A evap leak in the emissions. At first it told me to tighten gas cap. I replaced gas cap and it didn't solve the problem. My inspection came up months later. They ran a smoke test and couldn't find any leaks. So they replaced gas cap with the exact part from Chevrolet. The light was off for a little over a week and then came back on. I have replaced gas cap again with exact model part and had no luck. I have replaced the purge valve and vent solenoid before my inspection. Any ideas what the problem could be? Maybe the leak detection fuel pump?