Unfortunately, oil consumption in these engines can be quite large. GM has put out service bulletins which says that engine use up to 1 quart per 2000 miles is perfectly normal. I found some information on the bulletin:
(NOTE: - I was unable to find the actual bulletin, but the following is an excerpt from it, which was copied into the forum link I provided above. Scroll down to entry #3 to find the bulletin in it's entirety.)
Aggressive Driving High Speed or High RPM Driving
Aggressive driving and/or continuous driving at high speeds/high RPMs will increase oil consumption. Because this may not always be an everyday occurrence, it is hard to determine exactly how much the oil economy will be affected.
A higher rate of oil consumption is normal for vehicles equipped with manual transmissions that are driven aggressively. By "aggressive," we mean operation at high RPM (3,000 RPM to redline), with frequent use of engine braking (using the engine to slow the vehicle). Vehicles that are driven aggressively may consume engine oil at a rate of up to 0.946 L (1 quart) every 805 km (500 mi). This is normal for a vehicle that is driven aggressively. No repair is necessary. This characteristic does, however, require the owner to check the engine oil level at sufficiently frequent intervals, especially when driving aggressively, to assure the oil level remains within the recommended operating range. As the Owner's Manual recommends, you should check the oil level every time you get fuel.
While whether you or I feel this amount of consumption is wrong, GM doesn't seem to think so. It may or may not be a cop-out by GM in not having to fix the engines, but it is what it is. With the bulletin GM is saying to the consumer, live with it.
My suggestion to you is to ensure you are keeping up with the oil changes and ensure every time you stop for gas (if not sooner) you are checking the oil to see how much you'll need to add. Buy the oil by the case and call it a day. My 2006 Chevrolet Silverado suffers from the same fate, though not as extensive as what you are seeing. I use about 3 quarts per oil change. Since I use the oil life monitor to change the oil, I really don't know how many miles that is.