Thanks! So for the Yukon, I'm pretty sure the body lines are the same as the Tahoe/'Burban, so you should be good there, and you won't need to cut the flare in half since you have the XL.
However, these are "cut-out" style flares, which means they're meant for you to widen the wheel well by cutting and folding back the fender like this:
On the front we were able to just bend the aft portion of the flare. In the rear, since we were already cutting the flare in half, we were able to cut it so that it fit in the existing wheel well without cutting and folding the fender, but if you aren't cutting the flare, you might have to cut and fold like he did in the above video.