My 2002 Hyundai Accent labors has major problems shifting gears?

When the car is in park and idling sometimes the engine will rev itself; the reving does not stop so I usually shut the engine off due to being thoroughly freaked out as to whether my car is going to explode. Also, when driving the car won't shift into different gears for the appropriate speeds. When at a stop, I need to really press down on the brake to keep the car from surging forward. Sometimes the check engine light will go on and sometimes not. I have already had the transmission serviced(oil and filter) but it has not helped. HELP!!!