I have a 2013 Silverado 2500HD Z92 with an ALC lift and Mickey Thompson Baja's. At 4,000 miles tires were rotated when serviced. At approx 6,500 noticed both front tires were cupping on the outside. Left is worse than right. Took it to one garage they stated alignment was within specs. Took to dealership where the truck was purchased and they said that the Right Front was just slightly out of alignment. They adjusted to specs and tried to tell us that we did not rotate properly, which they did when serviced at 4,000 miles. When we brought that to their attention they tried to say that the roads that we traveled on. So, we left with nothing resolved. At 8,000 we went ahead and finally rotated and put the cupped tires on the back. Now at just a little over 11,000 miles they are cupped again and is worse now then at the start of this issue. What could be causing this problem? Alignment is good, had that rechecked, and tires have proper air pressure.