The "5 degree swing" thing is funny to me because I spent my first two years of brisket cooking treating that 160 mark like it was written on stone tablets. Pulled one at 165 by accident once because I got distracted yelling at my dog, and it was the best flat I had made to that point. Your uncle might be onto something with the thick part probe too, since I was always stabbing the point and wondering why my numbers made no sense. I still bounce between 160 and 165 depending on how the bark looks, so take this with a grain of salt.