You won't get better mileage with e85...that's not what e85 is about. You should buy it so we aren't depending on overseas oil as much.
Notice the differences in mileage between Gas and E85.
http://www.fueleconomy.gov/feg/byfuel/FFV2000.shtml
I don't know if my 2000 NBS Yukon 5.3L is E85 compatible. Does anyone here know?
www.fueleconomy.gov doesn't show Yukon's and Tahoe's as E85 capable until 2002. I thought my 2000 5.3L had the same motor as a 2002 5.3L