If you have the factory tow package, the wiring is all the same as you use the factory harness and attach about 4 wires.
The only difference becomes the angle of the brake controller. The Prodigy unit that I have allows a greater degree of freedom with regards to the angle of the controller than some other units. No matter what you choose installation should not take more than 30-60 minutes, depending on how quickly you work.
I have the Prodigy in my 04 Expy, jakermc is right it gives a lot of flexablity on mounting angle (I believe up to 75 degrees). I ordered it online from rjays.com, you can order a wire harness that plugs directly into your truck (if you have trailer tow package), for 12 or 15 dollars extra.
The harness they offer to plug directly into the factory connector is nice, only $10. I just traded in an '03 Expy for an '07 and need to move my controller over. Any idea if it will work on an '07? The website only lists compatibility up to 2006.