I had a P0449 code on my 2008 Silverado crew cab and used ACDelco 214-2082 Canister Solenoid Valve Kit to fix it. I did not need to use 5/8 heater hose as others have used, because with a little bit of silicon spray and a bit of wiggling and pulling, I was able to get the original hoses off in reusable condition. However, I did cut off the hose connectors on the bad solenoid valve and crushed them in a vise, which made it much easier to get them out of the hoses.
The valve is located in front of the gas tank under the middle of the truck on drivers side.