Tire Sidewall problems of the 2006 Mazda Tribute

Mazda 2006 Tribute awd 4 cylinder with 20,000. At 17,000 miles on it noticed all four tires showing sidewall wear and feathering on tread. Had car aligned by dealer, told car alignment was out by 0. 25 degrees. At 20,000 miles noticing cupping on all four tires. Driving 85% highway no off road activity. Noticing alignment was out after 3500 miles. Average yearly driving miles 20,000. Beginning to fell that there is a problem in front end geometry.