If the "jerky" motion was restricted to the Z axis, I'd say it was probably stiction, and advise more lubrication. But if it really affects all your axes, I'd have to say something else is going on. Are you sure you didn't change anything else? Is the G-code program you used one that you've used successfully before? Does it have a G64 command (continuous contouring) or a G61 (exact stop)? If it's in "exact stop" mode, then the end of every little line segment will jerk it to a stop before it continues on.