I have a 2013 Sierra with a little over 105000 miles . Body is rust free does have some paint flaking. In March at 100800 miles I we underneath for a gas tank sensor. I found a hole in the left frame rail, approximately 4 inches x 1 inch . I contacted GM . There answer was you perforation warranty expired November or 100400 miles which ever came first after several week they offered a service voucher for $100. I declined, I am going to keep fighting. The whole frame is in terrible condition. My 2008 has surface rust but nothing like the 2013.
I pressure washed the underneath the other day to make a repair. I found the rust to be much more extensive nearly 18 inches long. Disgusted with GM this is my 16th and 8 brand new GM product, probably the last