Everything I've seen for at least the NNBS Silverado/Sierra is mods in the under hood fuse box. The GMT900-based full size SUV is probably similar.
The fogs on the GMT900 is definitely BCM controlled though, so there is still likely a way to do it there if I can find some pinouts and locations. I've just been used to not having fogs for years so it really hasn't crossed my mind to even try this yet.