2.2 DTI loses sudden performance

Hello too, I have a 2.2 TDI Vectra EZ 11/2002, unfortunately he suddenly loses power in unregulated distances, you drive with 140 and he breaks away on 80 things. If you restart the engine after a short time it works again. The Opel dealer has already improved and replaced. Without success. Question: Does anyone have a similar problem? Does anyone know advice? What if my Garatie 11/2004 expires? Are there legal bases? I AM FOR EVERY REPLY OR EVERY TIP DANKBAR!!! Thank you very much!