Also just know that different GM dealerships deal with the aftermarket in different ways. I have one dealership that will work on anything without any issues. I have another local dealer in AZ that tells their customers that if they even add an axle-back exhaust it will void the warranty. I had another customer that took his supercharged SS in for just an oil change... and they black flagged his VIN# in the system for a complete void of the powertrain warranty. Now that's illegal but they do it anyways. To get the best answer you can always look at the "Magnuson/Moss Act" It should answer all the questions on what the dealership can and cannot do regarding warranties.
Just my .02
