Our 2005 will sashay around under hard acceleration and it isn't wheel spin. Even in third gear it will shoot off left or right as if the roads were rutted. It almost feels like something in the rear suspension is moving around causing some erratic rear steer. Our old Chevelle could break right loose going first to second and still go straight. Is this common to these cars? In first or second, it can break loose and I can tell when that is happening. With only 15k miles, things shouldn't be worn out.