found what turned out to be a common problem. my 06 1500 (54k miles)gave a 0449 Evaporative Emission Canister Purge Solenoid trbl code. behind fuel tank, attached to bed, there is a round black plastic can, with a hose and wiring connector. the plastic can's top can be removed and will probably have a lot of dirt in it. the solenoid can fail and mine metered open at 1.5 mohms. the new one was 20 ohms. part was $27. it was not the fuel cap. the canister can be cleaned, if your in a dusty enviroment- I would check it. hope this helps save some one else some money.