On you drivers side, in that little inch gap between the cab, and the box. You can see the top of your gas tank. Stick your head between the frame and the body. You will see a little black box, with a thick hose going to it. IT will be on a bracket bolted down. The valve solenoid whatever you want to call it is made up of black plastic. You can try and clean it out, by taking an air compressor, WHEN ITS OFF, and blowing it out, and also removing both ends from the charcoal canister, where the tube goes to, its a grey box the size of an xbox. Remove both ends, and then take your air compressor and blow the tube out too. Because there gets ALOT of dust and dirt and just junk in that. I relocated my solenoid to my engine compartment. You can go to a part store and get the same diameter hose and run it all the way up to your engine compartment. I highly advise that. If this is your problem, you must be getting terrible gas mileage. I know i did. I hope this helps!
Hey man if u dont mind me asking can u tell me where this evap canister and shti is that keeps getting clogged up... i believe thats why my truck is pulled a p0449 code. thanks