Yeah, in searching I found the same thing. Several different part numbers and parts. The one in your pics, in fact, is different from the one I ordered. Mine, from what I've seen in the pics has 3 wires.
From what I understand, my antenna is for the XM radio as well as the OnStar.
What I ended up doing is going to the dealer and getting the info (and price) on the correct part for my truck, then, you guessed it, using the inter-webs to see what I could come up with. I found the part, OEM GM part, on ebay for $70, shipped. The dealer wanted $240!
Now, I am one to try and spend my money locally when I can but $170 difference?! Forget it!