Q: I have two codes on my truck 449 and 455, it is running rough like it is missing on 2009 Chevrolet Avalanche

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It runs rough like it is misfiring at RPM's below 1000, seems to do fine at higher speeds. These are EVAP codes and I have doen the visual check of hoses and connectors on the cannister and solenoid and even replaced the gas cap. Everythins I read does not make a reference to the engine running poorly at low RPMs with thse codes. I am reluctant to start changing parts just as a hit and miss tactic.
(2) Answers
Did you ever figure this out? We are experiencing exact same issues in our 07 avalanche & when run diagnostic the codes are same as yours. Thanks