Came over to the 'dark' side last month after a long list of Kraut SUV's, sedans and sports cars none of which were completely trouble free but all in all no major issues.
The GMC is my first non German vehicle since 2002 with the exception of brief ownership of a 2010 Wrangler. So far, I'm as happy as a clam. The ride and build quality and technology are comparable, and in some ways better, to my most recent (2017) X5.
I considered the X7 and I'd expect it to be reliable and perform as expected. But I've always wanted a truck and the Sierra won out over Ford and Ram. And, in spite of current inventory shortages, the Sierra 1500 discounts were at least $7k better than the German rides.
That said, these mechanical beasts are just that and subject to malfunctions now and then. It's a real pain and in the case of the OP the issues were too many to bear.
Taking our first road trip next week and in October will tow a rented 28' Airstream to Florida. Anxious to see how the truck performs both with and without towing while road tripping. First 750 miles I've averaged 15.8 mpg with the 6.2 which is about what I'd expect from short trips. Would expect to achieve low 20's with no tow and low teens with the trailer.