[JSH]

The 2 inch lift on my Astro van didn't effect mileage in a measurable way - 17.0 mpg average the year before and 17.1 mpg the year after the lift.

Going from stock 215/70R16 tires on 16 x 6.5 wheels to 235/65R16 tires on 16x8 inch wheels dropped my highway mileage about 1 mpg. They are heavier, with 3/4 inch more tread width, and 1.9" larger in diameter. The wider wheels and different offset increased track front and rear by 4.45 inches. The better tires and increased track completely transformed the ride and handling. Much more stable in curves today with less body roll. The lift means I can do high-clearance forest roads without worry of bottoming out. (I dented the oil pan on my 2003 Jetta TDI)

EDIT: 1 mpg was 6%