This is the part I bought, which all the parts websites said is the correct part for my 2004 Tahoe LS.
But this two-piece kit is also available, althought the websites say this is NOT the right kit for my Tahoe.
Here is what I see when I crawl under my truck.
This is near the back of the gas tank. This rectangular piece looks a lot like the one in the two-piece kit above.
This is the Evap Canister mounted on the side of the gas tank.
One of the lines from the Evap Canister leads to the unit pointed to by the arrows in the next three photos. I can't tell if this is the other part shown in the two-piece kit above. Does anyone know what this part is?
Finally, this is a little more forward. I'm not sure what the arrow is pointing at, but I don't think it's part of the evap system. Maybe part of the 4WD shifting system? I have no idea.
Here are a couple of GM diagrams I found, and a couple of pages from the GM manual. I see there is some confusion between "purge valve" and "vent valve". The manual says the purge valve is under the hood, on the intake manifold. But I have looked at that, and the part I bought is much bigger. I think other GM trucks, especially pickups, have the part I bought near the gas tank. And I think what I bought is a "vent valve" regardless of the word "purge" in the name of the part.
Any ideas on what I have here?