I have the same problem with my 2006 Chevrolet Uplander after only 18k miles. I have Goodyear Integrity tires on my car. They are original equipment from the dealer. They are very cheap tires. I looked on the internet and found many others complain about these tires. You said that worn shocks can be one of the problems. I rotated my tires every 4K miles and my tire pressure was as GM stated on the door of my car. I take care of my car extremely well and believe tire companies look for ways to not live up to there warranty with reasons like cupping. When defective tire material or design are the real problem.
When I brought my car into the Goodyear dealership right away the manager rocked my car back and front and said it was defective shocks because the car did not stop immediately and had a slight double jump, then he showed me another car next to mine and it stop immediately. This car was a BMW with racing shocks and said they would not honor my 50K warranty because of my supposedly defective shocks. I brought my car to my dealership and checked another new Uplander and the shocks on the new car had the same type of restore after pushing the cars bumpers down to see how soon it would come to a stop. All 4 tires have cupping. I believe that Goodyear and other tire company have there employee use this reason so they do not have to replace all the garbage tires they sell. It's just another consumer rip off. I have a report from my dealership saying my shocks are in very good condition and this type of vehicle has soft ride type of shocks. My cars ride is wonderful at higher speeds (50-65mph) at low speed I feel the up/down bumping. The only thing I can do is take them to small claims court. This however would take my money up front and lots of my time for a few bucks. That's how these companies get away with not living up to there warranty.
