I am averaging 13.1 mpg and I mash it as much as possible! I only got 14 on my 6.0L Denali, that proves the H2 is an amazingly efficient engineering marvel. I remember the instant mileage display that GM used on older trucks, I could get it down to 4 mpg
Try resetting the mileage thingy! that always helps!
http://www.msnbc.msn.com/id/25051729/