AND READ your shop manual. In addition to the excellent commentary above, it could STILL BE the pump. There's a procedure in the manual by which you attach a vacuum gauge to the pump inlet. I believe a typical figure is that the inlet side of the pump should be able to pull in excess of 12" of vacuum.
If not already mentioned, check or replace old hoses, IE the one between the supply tube and the pump, and the hose between the sender and the supply tube.
