My experience is similar. My GTO used about 2 quarts in the first 5,000 miles. In the first 1,000 after it's first oil change it's down about a quart.
That's the worst oil consumption I've ever had in a new car.
GM + Aluminum block = Oil Consumption.
My wife's Denali has 50,000 miles on it and doesn't use a drop between oil changes (5K miles). It also has a GM 6.0L small block but, it's cast iron rather than aluminum.
The ten year old Volvo 850 Turbo I traded in for the GTO had 145,000 miles on the clock and likewise, never used a drop of oil between 5,000 mile oil changes.
If the GTO is using oil at this rate when new, I am very nervous about oil consumption at 50,000 miles when the warranty has expired.
I'm not so much concerned about the cost of a quart of Mobil 1 once a month. I'm worried that if I forget to check it for a while, the damn thing will spew oil to the point that damage could result. I've just never had to monitor a car that closely. At least, not since the 70's.