2002 Hyundai Accent Mystery problem

Transmission problem
2002 Hyundai Accent Automatic 47000 miles

My car was making weird noises when I accelerated and it was as if I could feel the car changing gears (even so its an automatic car). I got it serviced and he replaced the automatic fluid as well as giving it a good general service but the problem is still there only varied slightly.

The car just seems to rev a lot for no reason. For example even when I'm stationary at a red light or something it's revving and its like my brakes are the only thing stopping the car from driving itself.

I've also recently had my car registered and it passed the pink slip inspection- just not sure why the mechanic isn't picking up on this problem.

I hope that all makes sense. From the description do you have any idea what the problem could be?