Hi Rev,
Best I can suggest is to check your tank and pipe work up to the pump for leaks. If all is ok I would recommend changing your air and fuel filter and check your m.p.g. for a week or two after that. If it still no better and your engine is a high miler your next step is to have your injectors serviced ( I assume although your m.p.g. is poor you still have normal performance ? ) FT