2001 express van fuel guage doesnt work

I have a 2001 express conversion van, the fuel guage has never worked since we bought the van. About three months ago the fuel pump went out, I'm assuming the sending unit and pump are 1 piece. The guage still didn't work after the pump was replaced, anyways yesterday for some reason when you turn the ignition key to the run position the fuel guage will slowly start to climb then drop back down to empty again. we used to be able to tell when to get gas because the low fuel light would come on but that stopped working a while back.