2005 Yukon XL 4wd. I put new tires on the truck when I bought it in July. I have had it aligned twice now, but the front tires are wearing really ******* the outer edges. I don't go flying through turns, I drive it very gently. When I put the truck in reverse, the front wheels drag across the ground. When I put it in drive, the front wheels plow, causing lots of squealing. In fact, the front tires squeal at anything more than a slight turn. The alignment shop tested the ball joints, and confirmed they are good. The upper control arms are brand new. It tracks straight and true when driving down the road. I'm unsure of what else could be causing extreme wear on the outer edges of the front tires. The back tires look brand new with practically zero wear on them. The fronts look like they have been on the road for 10 years. Please help!!!