I have a 2003 GM 72K miles and both my front tires are wearing prematurely and cupping on the inside of both tires after 12K of use. The left (driver) side is worse. Took it to a tire shop for alignment and they said everything was perfect within specs, so they did not charge me anything. Since it's both sides I don't think it's a shock, or ball joint problem. Is there a common part in the front end of these cars that would cause this ? I hate to start shotgunning suspension parts. Tires are Toyo Supreme, 225/R60-16's not the best, but also not cheap tires that can sometimes cause this type of problem.