Thanks for the response. Not trying to add addition tow capability, but trying to get to the max capacity of 8300 tow. Everything I'm reading shows the standard tow capacity to be 6300 for the Yukon XL out of the factory, but there is/was a HD towing package option for my model and year that will upgrade a few things to handle additional weight. Larger rear axle, upgraded cooling, different spring on back, (which I think is what silveradosid mentioned above), et . Was just curious to see if that can be added after by the factory or if there is a way to add those after the fact?