fuel light comes on, but I got gas?!

:banghead: I'm a new member in need of help. I got a 93 concorde 3.5 and the fuel light comes on at times when i got gas. I'm thinking it came from letting my gas get too low. Now the RPM jumps up and down causing the car to hesistate and cut off while I'm driving. I have to mash the gas for the RPM to jump back in place. I have seen the cruise light came on maybe twice, but i dunno. someone please help me!