Frame Rust problems of the 2013 GMC Yukon

2013 Yukon xl was found to have excessive rust on the frame and other parts underneath the vehicle during an annual inspection. The wax coating if flaking off the frame leaving bare metal that quickly rusts. Gm claims that the damage is environmental and the issues is the salt used on PA roads. If this is the case, then gm should warn all customers that their vehicles are not built to last in the state of PA and that they will not honor their warranty. None of our other vehicles are rusting. Their are many other people complaining about the same issues and the problem has been noted to start during the first year of ownership before going through the winter. They have not properly coated the frame to withstand rust. I had to pay for undercoating now to rectify the problem. The undercoating installer mentioned this is a know problem with gm trucks and the company refuses to acknowledge or address the issue.