fuel guage and leak problem

Hi I recently changed my fuel pump in my 2000 s-10 becuase it went bad, but now the gauge will not go above 1/4 tank and it wont take any more than that as well. Do you think that this would be a bad pump, or is there something else. Also I noticed the other day when I parked my truck that gas started leaking out from under the truck near the tank. So, i crawled under there and saw it leaking from something that looked like a small box, about 4 inches by 2 inches. There is a hose going to it. I am not sure what this is, or if it should be doing this? Do you know? Thanks much