I have a 57 plate Vectra SRi 15ops auto with 19,000 miles on it. When stopping the car in drive and haulting there is a judder under the driver's seat. When moving off and depressing the accelerater the car jerks into gear which has now become quite annoying. However if placed into neutral and then moving off placing car into drive it will move off smoothly. I also have an intermitant problem where at low speeds in traffic around 6mph the car will start to jerk very slightly until speeds get going again. The dealer can not detect any faults but I have driven auto cars, Toyotas, and have never had this problem with an auto gearbox. Does anyone have any ideas as any help or knowledge would be greatly appreciated.

Thanks in advance,