B MV6 jerks at kickdown and from 180 K/mh

Hello, have the following problem with my MV6 Caravan/Ez: Nov 1994/ Automatic/270 tkm run /Inspection plus timing belt before 20 tkm new/ When I try to drive full throttle or to run a kickdown to overtake, the car/gear (?) is jerking and an acceleration is no longer possible. From driving I tried everything, tried all gears, TC on/off, S-button on/off, at several speeds… each time this braking jerking 🙁 –Now I know of light oil-lubricated … could there be too little gear oil? Or how would such a thing be noticeable? No fault is shown on the on-board computer… no lights on!!!! –gear damage? — Then found when searching around: suction pipe flaps defective? Bin mechanic, but I haven’t had such damage on stage yet! Someone’s experience with: Cost of parts, repair…? Thanks for opinions/tips/stimulations… Greetings Steve