Whenever my car is cold there seems to be a "slide" when the automatic transmission changes gear from second to third (or third to fourth, I don't really know :-) ). The engine revs up for a while and then the gear engages. This happens every time but only once - the first change when the car is still cold. Each next change is smooth and quiet and the car drives like a dream. What could be the cause of this? Can I just ignore it and enjoy the drive?

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1987 300E 185k miles