I have an 09 1/2 GT - the dealer says it comes with Active Fuel Management to shut down 4 cylinders on the highway. Where is the display to tell you if you're using 4 or 8 cylinders? All other GM's I've driven (Impala SS, Suburban) make it quite obvious. I do a lot of highway driving and I'm trying to get over 25 MPG.
Prior to starting the car press and hold down the left scroll (return) button on the steering wheel. Start the car while holding down the button. Once the car is started you can let go of it. This will put it into "engineering mode" and give you a large list of availble items to look at while driving (AFM, Throttle position, battery charge, etc.). Scroll through the list using the left scroll button and press it to look at the option.