gmc sierra evap error

[jg250]

I have a 2003 gmc sierra it has a 5.3 v8 4x4 sle. In the past year the evap light keep on coming off and on. I get a p0455 code. I have changed the gas cap. Recently in the morining when the truck is cold it runs very ruff. Like it gonna stall. Then after it warms up its fine. I am concerned about the major evap leak code that keeps on showing up. does anyboyd know what the problem might be and why it runs very ruff when cold but goes back to normal when warm. Can sombody please help me diagnose or give some suggestions on where to look.

 

 

Thanks

[Indy]

I've had evap codes PO449 and PO452 for about 4 years now. I replaced the gas cap and the evap vent solenoid and checked all the wiring and still it's not fixed. I read the codes every week or 2 to make sure nothing more serious has popped up. The CEL went off for about 5 days this winter when it was - 27°C.

My truck is running fine though. 1999 5.3L