[N5GKP]

Just a thought, have you looked at the reluctor rings on the rear drive shafts? If yours is the model with exposed reluctors they're prone to corrosion which can distort them & also damage the wheel speed sensors and cause 'flat spots' whilst driving. It starts off periodic but when it gets worse the car will jerk a lot at any speed.
Best bet is jack the rear, and have a look at the drive shaft reluctor near the hub, if it's noticeably shiny compared to the rest of it that could potentially be the issue