07 3500 170 wb CRD 13,500 miles.Tires rotated twice. All six have 4 to 5/32 left. They need to be repleced. I am shocked. I was told i would get twice the life out of a set of tires. I owned an 03 2500 sprinter 158in wheel base and got 20k on the rear and over 40k on the front running goodyear. Tire brand is Continental. I never ran them before so i dont know if they are junk or not they are OEM. Tires are wearing evenly across. Anybody having this problem? Is this under warranty? Should i contact the dealer?