What type of AC motor. Brush, brushless, induction,etc..
Electronic power steering does not use Power steering fluid. It uses electric motors and sensors to assist steering. Yes it might be any of those problems. Have you had a mechanic (not service manager) ride with you while you drive the car? I cant see how a tune up will have anything to do with it though, since you have electronic power steering. I would look into the torque sensor or the eps motor.
