Anybody experience this?

When I hit approx 55MPH (90KPH) and maintain a constant cruising speed, there are small jerks in the car that I can feel. Happens quite frequently.

I recently had into the dealer for rough, sluggish acceleration when it's cold and they cleaned the throttle body.

Is my transmission slipping or could it be the motor causing this?

 

FYI for anyone that this may help. Turned out to be the ETM. Dealer replaced it with a new one under warranty. Car drives like brand new again!! Smooth idle, better acceleration etc.