Doug, don't forget to factor in the reduction in gearing therefore the reduction in the odometer mileage as well. IIRC there's a 12-13% difference in size from the stock tire to the 33" tire. This means you're actually travelling 113 miles for every 100 miles on your odometer unless you've changed out the speedometer gear in the xcase.

I'd check your speed using a GPS then factor the difference into your mileage calculations. <img src="/forums/images/graemlins/kewl.gif" alt="" />