Tires

I have 2000 Chevy Silverado 3/4 ton 4 by 4. It is used about 95% of the time on the highway. It only has 38000 mile son it and I just put the third set of new tires on it. The last tires were Cooper Discoverer LT. They were replaced with Cooper Discover AT's. Has anyone one had a problem with tire life and any experience with these tires? The tires all wear very evenly and the tires are never spun on the truck.