I have a 17 XL SLT and bought it with the factory 20" Conti tires and had gone from a 2011 Suburban and the ride in the 17 was night and day...I could not believe how much more solid and quiet it felt, and then I swapped out the stock 20's for my 22" wheels which I love the look, but in all honesty the ride with the 22's absolutely sucks...I feel more road for sure and it is noisy hitting bumps etc...just feels rough. The 20" tires really absorbed more road conditions and gave it a smoother ride. I would be willing to bet that if you were to experiment with a set of 20" wheels and tires you might see a big difference. Probably easier said than done, but maybe the new dealer you went to could try a set to see. Just a thought. I know these trucks look so much better with 22" or bigger wheels, but some of the 20" styles are not bad, and for sure the 20's have a smoother ride. Someone mentioned reducing the air in the 22's, also you might want to research the tire brand as well? Maybe another tire brand with a softer compound could help? Just a thought.
On another note, I lemon lawed an Acadia after 3 years, and it was the recommendation of the Service Manager at the Dealer I bought it from, for almost a year I went back and forth with GM about a solution with the vehicle and they only push you to the point of where you are now, get a Lemon Law Lawyer and they will take care of everything for you and you will get back every dime for the car...I even got paid for the window tint and 3 years of Registration. I went through a firm here in CA. called Norman Taylor and Assoc. and they took care of everything, and provided me a check less their fees that were about $3500-4k, but I put $11k down when I bought the car, and got back a little over $16k after their fees were subtracted from the settlement buyback, so since I got back more than my down and I drove the car for 3 years, it was a win win.
Hope this helps! Good Luck!