On my last oil change, my dealer gave my rear brake pads a need replacement soon with only 4mm remaining on the rear brakes. My front brakes were given 5mm. It is only front disk. The vehicle is a 2008 Chev Silverado 1500 4x4. The mileage was just over 15000 on the oil change. Is it normal for the rear brakes to go out before the front brakes? I was told I should get 40,000+ out of the rear brakes. Is this true? I do not do any towing but there is a lot of hills. I can also feel a sligh lock up on the rear brakes when going from drive to reverse and vice versa. Any help would be great