Hey Tony,
I’ve owned an 18’ Denali Ultimate with the 6.2, for about 14 months now since it was new(July 2019)and haven’t really experienced any of the issues you’re dealing with. The only time the radio is slow to change is when I’m playing music through my IPhone saved music. Other than that the radio is fairly quick to change stations. The retractable running boards have been great, no problems whatsoever even in slushy ice conditions. The object avoidance, parking sensors did give me a lot of issues whenever they’d get snow or ice around them. The message would come up on the information cluster saying “ park assist disabled “. The lane departure or lane keeping device works awesome, but kinda freaked me out on the test drive when my wife and I took the truck out at dealership for the first time. Thought an alien took the wheel....lol.
Hope you get some help at the dealership. Good luck...