I own a 2015 Yukon Denali XL and have 99,000 miles. I mainly use it to tow a camper trailer. I had a lot of problems with shudder in the transmission until they replace the fluid with the newer and heavier LV ATF Mobil synthetic fluid. It takes about 20 quarts (over $400 with 2 hrs labor). I have had that done twice. I have the 8 speed transmission. At 80k front air ride shocks were replaced $2,100 and engine oil cooler lines and trans oiler cooler lines, both for $980. I have had door "applique moldings" replaced several times for over $300. Front brake pads and rotors replaced at 65,000 miles for $450. At 56,000 miles i had the valve lifters go out and it cost $3,250 to fix. That happened as I was towing the camper on a vacation. Three day delay in the trip. At 55,000 miles the AC condenser went out, but that only cost $475 to fix. At 45,000 miles $390 to change fluid in transmission per bulletin 18-NA-355.
I haven't added it all up, but I have spent more maintaining this vehicle than I have on all my other vehicles since I first started buying new vehicles in 1968. I like the vehicle but this is my last GMC vehicle ever. Nothing was covered by warranty except a battery in the second year. I have done all the required maintenance at GMC dealers.