I am not sure but could it be an issue with the "Clutch release bearing" or something to do with the turbo. Does this jerking issue happen at specific RPM's or is it specific to the 2nd & 3rd gears? here is a pic of the clutch release bearing in a m800 gearbox.
image
Some cars come with "Hydraulic clutch" like fiat palio, in such cases you can also check the hose that connects the release bearing with the pedal. Sometimes the service center guys will know the problem, but they act like as if they cant find the issue at all.