Mercedes ML 270 diesel auto. When I try to kickdown to overtake etc, it goes into 'safe mode' revs high but wont go above 40 mph. If I stop, turn off and then on again it runs OK. Seems to be OK if I drive really cautiously, but as soon as I put foot down hard, it goes. I have had new filter, seal, oil done this week, but is still the same. When I am towing my caravan, the same thing happens. When changing up (I think from third to fourth) it gives a spurt from about 2000 revs to 3000 then changes normally.