Hello everybody,
After a two month plus backorder, I was able to get my 2.5" (4" total) BDS lift kit on my AT4. I kept the 18" wheels (-12 offset on 9 in wide) and put on 35x12.5" Nitto Ridge Grapplers. I trimmed a small amount on the front lining due to rubbing at one angle. The bigger issue was in the back that required some trimming of the bracket. Even then, there was a tiny rub that probably would have gone away after a few miles on the road. A couple small hits with the hammer on the bracket allowed the tire to clear without touching. The ridge grapplers are almost a true 35" (actual 34.76") and I think if I had gone with a tire that was 34.5" there wouldn't have been any rubbing on the bracket. You'd still have to trim the mud flap I imagine. If you are concerned and want to give yourself room for error, shoot for ~34.3". The front may be affected more with a stock front bumper, as I have a replacement. The guide on the internet is fairly accurate, but I did not take the bracket off. Just heat and cut.
https://wheelsasap.com/gmc-at4-oversized-tire-trimming-guide/
I didn't take pictures of the bracket/flap rub on the back, unfortunately. Hope this helps.
JR