Im pretty sure the canister is on the passenger side down low and looks like a toilet ball float. There are vacuum lines that run to and from it. You can follow a line from there to the collector (might have that name wrong) in the back of your truck above the spare tire. See if you can find any lines that are disconnected or cracked.
01 XLT 4x4, 4.0, 4.10 LS, Auto, 32's for summer, Toolbox, E-Fan