I have two codes on my truck 449 and 455, it is running rough like it is missing

What is your question?

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.