I need help. I have a 1984 GMC full size Jimmy 4x4. When I apply the brakes ithe front end shakes, real bad sometimes. At first I thought my lug nuts were loose. Not! I tok it to a well regarded suspension place and before I could finish describing it he told me it was the front rotors. He says they're warped and need to be turned or replaced. Sound about right to everyone? What could it be?