While driving my Octavia mk1 1.9 tdi, after reaching speeds of 60 km/h and above it starts to misfire with heavy. Jerking. If I drive below that speed it drives normally, and I don't notice any symptoms and i ideal. I already changed the diesel filter and engine mount. The mechanic suggest that it could be an issue with Diesel pump or possible the clutch. I would appreciate some clarification on this.