I have heard for years that these cars eat money. I still wanted one but couldn't pull the trigger. You have found this out the hard way. Tires and transmissions seem to be the universal problem. I can't speak for the codes or alignment issues. I would have turned off the AFM as I was leaving the dealer; the mpg isn't worth the sticking rings/oil consumption problems. Surprised to hear your Bilstein struts didn't hold up. My GT eats front wheel bearings about every 6 to 9 months. Your GXP may have demons.
I sat in a Regal when my car was at the dealer a few months ago - hit my head getting in and out. A Lacrosse with the 3.6 (300 hp) would be a better fit for you and they are plentiful should you decide to bail. The 2013+ Buicks are certified for 6 years, 100,000 miles - give you something of a breather.
