Early model 2000/2001 gals used up some of the components from the mk1 - we had this situatoin and if was found that there were some incompatiblities between sender and fuel gauge - Ford eventually change the instruments which got rid of the problem (not quite the same as yours) under warantty despite it being out of warantty by the time they resolved the problem - may be similar to your prob though some discussion here alternatively do a search with " slow, fuel " and my username - will get some hits