1999 GMC Sierra 4.8 Liter running funny
 

Hi, new to the forums. I had some truck problems and it is idling funny. I did a code tester to it and the code came up P0449 Evap Emission System Failure and I was wondering if someone could enlighten me if this could be the reason my truck is running funny. Is it worth getting the part for $200 or would it be something else causing the problem? Any suggestions or comments would be greatly appreciated.