OK, so when I got my Yukon a few weeks back, I noticed that there was a sticker inside the lift gate that says something to the effect of air springs installed. It has a min psi of 5 and a max of 35. These are not the auto ride, but they have manual valves down by the spare tire. I understand what they do (lower psi = better ride for the most part and higher psi = better for when you have a big load), but I am just curious if that was something from the factory or if the previous owner had those installed.