I agree on the tyre size - the gearing is the main issue, which in turn makes the fuel economy even worse...
Also... don't forget that the front axle will be out of line - which means getting an adjustable track bar, track bar relocation bracket or getting the standard bar extended/modified. Then recentring the steering wheel. Don't go for a Warrior trackbar - there are completely shite - I bent two and a mate had one sheer completely...