My old man has a Yukon Denali. I think it is a highly similar vehicle. 2002 GMC Yukon Denali.
REPLACE CABIN FILTER. The climate control goes straight to hell when that SOB clogs.
What engine? At ~120k, the throttle body will need to be cleaned. You'll know this when the idle gets rough. Literally, crap builds up around the throttle body, restricting airflow.
Could need intake manifold gaskets at same time as throttle body. Just plan on pulling the intake manifold, cleaning the major components and replacing all gaskets.
Light bulbs go out probably once a year. However they are REALLY easy to replace. Hell, you might even have to put your beer down during the bulb replacement.
If you buy, practice removing the spare tire. Whomever came up with that system probably needs to be castrated to prevent the dumbshit gene from continuing.
What tires? Some of those trucks had Goodyears Wrangle HPs which SUCK GIANT COCK. You might as well have dog turds for tires. Go with Michelin Cross Terrains. They'll last about 80k on these trucks.
CHECK FLUIDS. Over time, (like, 3 years) they'll just burn a little bit. If you check everything once every 3 oil changes, you'll be golden.
CHANGE FUEL FILTERS. When that fuel pump goes...it goes. Ours went around ~150k. When she was done, she was done and the only way outta that was a ride on a rollback and paying a stealership in another state A LOT of money to fix it. As you can imagine, the womenfolk in another state with the borrowed truck and it broken down...did not go over well. I'd recommend replacing the fuel pump before that, maybe 100k or so (I think all fuel pumps should be replaced at that time).
Wheel studs break. Be prepared for this. Or at least my dad broke his. He does have a "special" touch with vehicles
.
When the auto-dimming mirrors go out, they are an easy replacement and you can get a new mirror for under 100 bucks.
To be honest, it has been a very, very, very reliable truck. A DD since 2002 and overall a badass rig. I am convinced it is the best SUV available. Minimal down time due to breakage, very easy to work on and ungodly comfortable.
One thing is that the MPG sucks giant donkey cock. I mean, oooph.
I've wheeled that truck everywhere. Mountains, Uwharrie, OBX and used it as a chase truck for the Sandblast Rallye (actually drove around on the course). She is a beast.
Towing is actually great. If you don't tow regularly, it works great. She can handle a built rig with minimal problems. Anything lighter and you can't even tell it is back there.
Of, GM made it VERY easy to add trailer brakes. All you gotta do is buy the control unit and a wiring harness. Plug in, setup the controller, done.
If I needed a full size SUV for fulfilling the role of being a general badass machine, then I wouldn't hesitate.
Otherwise, keep up with routine maintenance and that truck will serve you well.