Upgrade on OEM Stereo

[WCP1973]

I recently purchased a 2004 Sierra 1500 SLE Crew Cab. It has an older double din stereo with CD and cassette and the factory Bose system. I would like to upgrade to a touch screen with navigation. There are a couple listed on ebay..:Part #, 15204335, which is the one I think will work. Will I need to buy any other parts to make the radio function properly, most specifically, the navigation function properly. I have heard conflicting stories on needing to buy the gmos 04 wiring harness as well as a steering column module. I thought that since it is an OEM factory system, the wiring inputs would be standard on the back of the stereo. Any help would be appreciated.