I agree with the check your breaks idea. If its not that, I had a similar problem with my 04. It went from 190-200 miles per tank to around 160. After doing everything you have tried with no help I cleaned and recharged my K&N filter. I was back up to 190 miles on the next tank. It had been about 12 months since I last serviced the filter with lots of riding in the rain in between.