My book (for the 3.8) says : EVAP canister purge solenoid: "Top rear side of engine"....without any drawing or photo.....
Part is exactly same for '93 3.8 and '96 3.4.....
Other readings about 3.1/3.4 seem to point to same area, that is, near intake manifold.
HOwever, "Wikianswers" to same queston for transport 98 says "it is under the vehicle fastened to the frame near the fuel tank. It is a rectangular shaped black plastic box with a few hoses and lines connected to it. The lines are connected with quick connectors, and there are some going to the fuel tank and some going up front to the engine."..
...that is same engine as '96, but not same body..I have doubts..I think Silverados are like that.....but please report findings.