I just got the same code last week. It usually starts as a gas cap message on the dash and eventually lights the check engine light. I have cleared it twice and it keeps coming back about 5 minutes into driving. I planned to get a new gas cap but I do no think that is the problem. the truck only has 60k and most of that is highway, Relatively speaking that gas cap has not had many cycles of use....
I am curious how this turns out for you. I think I need an emissions test this summer for plates and need to get rid of that light.
2005 Colorado LS Ext Cab Z85
4x4 I5 5 spd 3.73 Auto Locker
Victory Red w/ color keyed facia
All the power options and sunroof
Stock at the moment