The Tiptronic transmission jerks sharply when the transmission changes from 3rd to 2nd when slowing down in its usual automatic mode, and also to a lesser extent on the change up from 1st to 2nd. It is most noticeable when slowing gently. It has been back to the dealer under warranty four times in the 4,000 miles since new for "software upgrades", plus an expensive-sounding Mechatron valve and control unit replacement at the last visit. Each time it is OK for a week or so, then reverts to the same jerking behaviour. Anyone else had this problem or know the solution? It's getting boring and spoils the whole driving experience of an otherwise nice car.