hi folks wondering if anyone else has had this issue and could shed some light on what to do next. I have an 07 ls and recently engine light came on, got the code reader and cant remember code but it was faulty gas cap or purge valve and evap canister. both were changed with oem replacement parts. light stayed off for 2 months but then started getting message on dash to tighten gas cap. checked it every time and it was tight no issues. now light is back on with same code coming up. any ideas as to where I should go from here. don't really want to buy another factory cap for 45 dollars and find out again that this does not fix problem.

 

When this happened on my '98 I had to replace the filler tube on my gas tank

 

The cap may be bad. Not releasing the tank pressure. You can go to any auto parts store and get a cap for much less. You should also have the Evaps system checked again.
When I bought my 02 SS, there was a Locking gas cap on it. Those caps do not allow enough of the pressure out of the tank. And gave me an Evaps code. Once I got a non locking cap, from Auto Zone, the code cleared and I have not had and Evaps code since. It's been almost 3 years.