I just bought a 2002 audi A6 2.7T. It has a code p0431. There seems to be some sort of power leak. The gears are not shifting properly, or at right time, I feel like its dragging for longer. Above 20 mph, I feel like something is over-spinning, and not enough power. What could be the case? is it catalytic converter or is there some sort of exhaust leak??? There is no engine noise at idle, nor any vibration. the symptoms starts above 20 mph. There is no vibration, just feels power leak. Only one code shows up which is p0431.