John, my '98 +4 gauge never got much above 3/4 when the tank was full either...
On my 4/4 the gauge does almost read full and there are still 8 litres or so left when down near the 'E' mark. After last week's trek, when the tank eventually needs replacing, I will try to fit a larger tank (it's only 9 gallon at present).
Cheers,
