I have an '07 Trailblazer, 208K on the odometer, and from day one have been using Full synthetic oil, until recently. I am in fact using an average of 2-4 qts. of oil in between changes. My mechanic has said basically these engines are notorious for burning oil as mileage increases, a lot of "slop" develops internally. His recommendation is to switch to the semi-synthetic blend, as it is better (and cheaper to refill). He feels that the synthetic is too thin for the slop and hence gets past the rings. I have only just done this with my last change, and while it still burns the oil, it was cheaper to refill, and cheaper than a major engine overhaul.....hell, my '07 Impala SS (305-8CYL) was burning oil at 90K, so I am not surprised by my Trailblazer.......maybe GM needs to look a little deeper at these issues long term.....