We have an '05 and see the same differences with the on-board computer vs hand calculation for mpg. Although there are times the computer is higher, most of the time it's been lower. Generally it's less than a 1/2mpg, but there are times it's as much as 2 mpg (either way).

C&J the Gas Pirates

I'm the Captain of this ship and I have my wife's permission to say so.