My S-line Avant with the S-Tronic has become really sluggish. It is at 26k miles and has had its services etc. I know the S-Tronic is known for being a bit slow in responding, but recently it has got a lot worse. Even in S mode it has become noticeably slower to react and even quite jerky when setting off. Is this normal? or should I be looking to get it booked in, for Audi to tell me they can't find a fault?