I was wondering if there was a hissing (esp. under revs) from your exhaust as a sign of a blockage, but after seeing your fuel economy I'm thinking there is nothing wrong with your bike (except return line - burrito syndrome) it's good for a high performance engine in a harsh environment.
I'm thinking your fuel economy should not be improved by the previous owners fuel since the fuel you put in should be measured against the distance that has been travelled, not the distance that will be.
Maybe clean the speedo sensor. In fifth gear the speedo and rev needles should be parallel at all times.
Do you fill your bike while on the centrestand? I fill mine on the side stand, to the lowest point of the filler neck, so the burrito is above the fuel line. Also, if full on the centrestand, I wonder how much the fuel expands as it heats up, because that would mean adios amigo out burrito.