96 Oldsmobile cutlass supreme rpm problems?

I was driving my car earlier and all of a sudden it wouldnt go past 20 mph even when pushing on the gas all the way and then it died. i started the car back up and thought id put some gas in it since i only had a 1/4 tank in there. i did that and then it started doing the same thing again. i put the car in park and reved the engine. when it gets to 4 it jumps back and forth from 3.5 to 4 rpms when i hold the gas down. any ideas on what the hell this might be?!?!?! thanks.