According to this youtube video from etrailer, you may already have the factory installed wiring for the brake controller like the Yukon, but you just have to find the wiring bundle underneath the dash and hook it up. I guess you can check to see if there is indeed a power wire located in the engine compartment by the fuse panel as the video implies, and if so, then you should indeed have the wires inside already.
Hope so, as that would be too easy.
Installation of a Trailer Brake Controller on a 2013 GMC Yukon XL - etrailer.com - YouTube
EDIT: They show a 2011 Tahoe, the same way, but more detail where the wires may already be.