I have a problem with my 99 chevy 4 wheel drive suburban. The car does not do this sitting still and putting the tack up to 1500 to 2000 while turning the steering wheel. But when I drive it,while starting to turn the steering wheel in a gradual turn, the steering wheel suddenly pulls away for a second. I then grab the wheel with both hands and continue turning. The rest of the turn it is okay…It does not do this in a sharp turn. What is wrong?