Brake Disc Pads problems of the 2008 Chevrolet Suburban

I purchased this car in may 2013 with 76,000 miles as a certified used vehicle from a gm dealership in NJ. I noticed on test drive brake vibration from the front. Before I picked up the vehicle they replaced new rotors and ceramic brake pads. Now at 17,000 miles later there is vibration again, once again the rotors are warped but the pads are perfectly fine. The service manager told me and I quote "it must have been a hot day and you took the car through a car wash warping the rotors. " if gm is making their rotors with non-virgin steel this can happen. I have previously owned a 2005 Suburban with 100,000 miles, the rotors never warped and I only needed them changed once at 55,000 miles, I have a light foot. In 2010 I changed my 2005 Suburban for a 2009 Buick enclave this car was the first time I noticed in the 3 years of ownership that I needed rotors twice, in 3 years I had only put 30,000 miles on the car, so that lead to the purchase of the 2008 Suburban. I can't help but believe there is something wrong in the making of their rotors, they changed manufacturer maybe?? with this 2008 Suburban I have also contacted them with no answer or reply to the fact when my 12 year old son who weighs 108lbs sits in the front passenger seat the passenger air bag light is on one minute and then off the next minute. Sometime I can put my purse and a gallon of milk on the passenger seat and the air bag light is on will display. Yet my 108 lb child or my 86 lb child the air bag light will go from on to off. So they are my two safety concerns, the rotors warping repeatedly and the air bag light not working properly which gm has refused to comment on. Thank you.