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

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.
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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
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