duffman
i also own a gs450h here in the u.k since may 2006. i have now covered over 20,000 miles and have never got less than 26mpg. on a run i would expect to get around 34mpg in summer months & around 30-31 in the winter.
suggest you talk to your dealer about your mpg figures, how are you finding the car apart from the mileage problem?
signboy