Les,
Congrats on the new car.
I've researched this topic online, discussed this with my cousin (diesel tech) and most say the factory installs regular API spec oil with no special break in additives on most vehicles.
Having said that, we recently purchased a Ford Edge Sport for my wife late last year and the OLM showed a 10k OCI even with the factory oil. I decided to change the factory oil at 3k miles and the logic there is to allow enough miles to complete the majority of the break in and then to dump the factory fill. Her car now has 6k miles and I'm going to perform another 3k mile oil change and then go by the OLM thereafter. Ultimately you should do what makes you sleep good and I believe most people who care about their vehicle's longevity performs an early drain.
More importantly is to use a Dexos rated oil.
Good luck with the Chevy...Those are nice looking cars.
