GM has always used narrow 6.5" wheels. Just be aware mounting a tire with a 7.5"+ wide tread on a 6.5" wide wheel can have the tire riding the center of the tread especially when pumped to those high pressures needed for carrying a load.
Load carrying tires work at their best when the tires tread matched the wheels width unlike a vehicle that doesn't carry heavy loads ie; race cars...drag cars...off road vehicles/etc.
Get with a experienced truck tire dealer that sells lots of tires to LDT owners. Good ones can give you pointers on load carrying tire/wheel tech.