1999 Pontiac Grand Am Grand Am that wants to GO!

I have a 1999 Grand Am, it has been wonderful up until the past 6 months. I had just gotten the powerstearing pump replaced (twice) and my abs light likes to flash and beep at me. Although the main concern of mine at the time is on random days my car decides that it wants to GO! I"ll start it up and it will run loudly (a revving sound), then when I put the car in drive it 'jumps' in gear and I have to hold the brake down as hard as I can and when I release the break the car accelorates at a very fast rate. Also while my car is in 'this mode' i'll be driving down the road and let my foot off the gas and my car will keep going faster and faster. When I place the car in park it will rev up to about 3 and sound like a race car. I've tried pumping the gas hoping that it was just stuck, there is nothing under/or in the way of the gas petal. When it's doing this it accelorates very quickly and it is very hard to stop if you have to stop at a stop sign or light, you have to hold down the break as hard as you can, then when you let off the brake the car races off. If I let the car go after a complete stop it can accelorate upto almost 40mph in no time without touching the gas.
I had someone drive the car yesterday while it was doing this and they were just as confused as I am. This has happened once this week and it happened once last week.
If you have any suggestions i'd love to hear them! Thank you so much!