Not much help, I know, but we on the MEG site this side of the Atlantic have had a post running for a couple of weeks re: petrol mileage.
Most of us running stock V6s, ST24s (170bhp) and ST200s (200bhp) are getting about 28-31 mpg.
I can't think of anything that would cause your consumption to be so high.
Set fire to it and make an insurance claim.
Then buy another one.
BTW what are these 'gallon' things? I read somewhere that they're like litres but bigger...
