Tire Tread/belt problems of the 2005 Toyota Sequoia

The dunlop at20 tires on my 2005 Sequoia have been wearing excessively on the edges from the time that I first purchased the vehicle new. I have had the tires rotated, and the front end aligned at 17,000 miles to try to slow down the uneven wear on the tires. All the servicing was done by the Toyota dealership in frederick, MD. With 27,000 miles on the vehicle the tires need to be replaced as the tread on the edges have worn to an unsafe level and I can't corner the vehicle without the tires squealing. This seems ridiculous in that the tires were properly cared for and the vehicle was maintained and the tires have prematurely failed.