My wife has a 2002 duramax crew cab short bed and when you come to a stop it is fine but when you let off the brake the back clunks and feels like the back drops or the axle twists back any ideas. this is realy strange i hope it is not the transfercase ower 1974 blazer seems like the same thing but it is old and worn out. I just replaced the little plastic pads on the overload spring to try to help but no difference. HELP!!!