Welcome to the forum from Iowa. Post up some pictures of your Denali.
As for 100K maintenance, in addition to plugs and wires, belts and pulleys, I would suggest you change out all your fluids if you have not done so yet. This includes flushing your radiator, at the minimum dropping your transmission pan and replacing the filter, changing out your transfer case fluid as well as your differentials, brake and power steering. This will get you to a state of known life on these things and will help keep your investment running well for a long time.
Word of caution, when draining your differentials or transfer case, take out the fill plug first so you know you can get new fluid in before you drain the old fluid out. The front differential can be a tough nut to crack.
Also, 100K is about the average life span for your rear air shocks and compressor so I’d start budgeting for new ones. Arnott makes some good aftermarket ones that I’ve been happy with on my Denalis.