Chuck:
I respect your knowledge and experience highly. You are a fount of wisdom. But after working with GM for over 28 years, I've learned that their powertrain engineers are often times ... well, optimistic. Their spec of 5W-30 is more of a "safe bet" than one of engine longevity. At any temp over 32F you're much better off with 20W-50.
I first learned this from a NASCAR crew chief. The proof? My Toyota 4-Runner just turned 350,000 miles on this oil. I even toss in a bottle of STP once in a while.
Sorry for being a bit off-topic.
