I have been tracking mine in a spreadsheet and I get 260 to 290 miles on 13.5 to 14 gallons. Average is 20mpg to 21mpg city driving. On the highway I get 23mpg or a little more.
And yes, the P0335 is the crankshaft position sensor. If you are getting the code you should change it before it fails at a bad time, or be carrying a spare and the tools to change it.