Look at this TSB. Go to step three, do you see the little round canister( filter)
The bottom hose coming out of the canister goes to the evap solonoid valve. Disconnect the hose coming from the filter then turn the valve about a 1/4 turn then pull it out. There is an o-ring sealing the valve to the evap box, make sure that comes out with the valve. If the new valve does't come with the o-ring get that too. It should be replaced with the valve.
http://www.clubtitan.org/forums/atta...4&d=1189618447
You don't say what year your truck is, If it doesn't have the filter you should install that too. Just perform the whole TSB.