Facing the same issue of gear jerk in vitz 2005.
But this issue appeared after a ghatia mechanic changed the temperature sensor under gear box chamber. He did nothing except open the gear chamber and close after temperature sensor replacement. Mechanic top up the CVT Oil and mix the old 3 litre oil with 1 litre new cvt oil.
Plz guide any one what can be the reason of forward and reverse gear jerk just after initial acceleration keeping in view above scenario.