The five year/100,000 mile warranty is irrelevant to the vast majority of people. How many forum members actually put 100,000 miles on in five years? When I bought my "lesser" 2015 Silverado the salesman kept pushing me to buy touting the 5yr/100k warranty and the fact that it would be gone for 2016. When I told him my 10 year old trade had 89k miles he had no response. It's just not that big of a selling factor. A lot of people trade more often than every five years anyway. I could see where the extra warranty would be of value if you were full timing and criss crossing the country and moving often.
GM is also cutting the 24 month, 24,000 mile maintenance plan to 12 months, 12,000 miles. Is the cost of a couple of oil changes going to change your mind when you are hard pressed to buy a vehicle for under $30,000 these days? A diesel tow vehicle is likely upwards of $50,000.