What is wrong with my Dodge Intrepid?

I own a 1997 dodge intrepid, recently i was driving it down a highway and i heard a sound under the hood, ever since i heard that sound the transmission or gear shifting has been messed up, sometimes i would be driving and the RPM's would go up but my car wouldn't speed up then the vehicle would jerk forward, when you shift from drive to reverse or reverse to park you hear a rough sound, the RPM's go up alot when you are bareley going that fast, id be going about 40-50km/h and my RPM's would be at like 3 or 4, i haven't taken on the highway since and i would like to know what's wrong with my vehicles gear shifting or transmission or whatever the problem may be, please help anyone? Is there anything i can do to fix it without taking it into a shop? I checked the transmission fluid and the oil and everything seems to be fine.