well how much fuel do you fit in when the DIS says 0 miles (or close to zero)?
Its a 12 gallon tank on a FWD iirc, and when ours got right down to 0 miles we could only ever get about 11.2-11.3 gallons in there (which when you consider the filler neck and pipework etc means theres probably still at least gallon in there when it says 0miles.
If your sender is dicky, maybe it shows empty with more than a gallon left?
I always calculate my mileage manually. reset the trip meter when i fill, then work it out when i next fill using mileage and fuel added. It'll do about 34-35 on the motorway, 32ish mixed and 28-29 around town.