Your truck is awesome!
I just had the 4” Fabtech installed on my Sierra Denali yesterday. I am running 285/55r22 Terra’s on stock oem 22s with a 1.25” spacer. I have rubbing inside the fender well closest to the cab.
I was told by the shop that the wheel spacers were not needed for clearance so I’m going to have one removed to see if that alleviates the rubbing issue.
Did you do any trimming or alterations to the back of the fender well?