Thanks boys for the reactions so far

Thrustwasher where is that? is this in the aut.xmission itself, no there where no particles in the sump of the transmission, changed also the cardan oil (cardan is the small gearbox at the rear of the car)
Sometimes it looks the 3th gear is the problem, example : I start to drive than it shift to the 2nd gear , after that it will shift to the 3th gear at approx 50 km/hour but when I backup my feet from the gas just before the shifting is made, you feel a(loud) boink in the car however the shifting is made to the 3th and in mine oppinion when you back up your feet the shifting should not be made, (because it was still in the 2nd).
I don't no how to say this in english but it look like sometimes there is a hangup in the 3th gear. it should shift but it won't do it at the right moment.
I hope the story is understandable

because i hope the problem can be solved, I will make a readout of the computer later on.
Thanks in advance
best regards,
Peter