I have an 2007 A3 S line Quattro with the 3.1 engine. When I put it in reverse, the transmission/ clutch seems to slip, grab and be sluggish. Engine will rev to 2000 rpm and the car will barely move. If I put it in gear and wait several seconds it will move in reverse, without slipping, at idle rpm. Forward speeds are no problems. The dealer serviced the transmission, dropping the pan, replacing the filter and fluid, about 100 miles ago but that has not helped so far. Any ideas?