the Z06 has a .56 6th gear. The standard C5 and Fbods have a .50 I believe. I got around 29mpg on the freeway bonestock, a/f around 11.9/1. After a .591 lift cam and getting it tuned to a 13/1 a/F, I am getting 34mpg cruising 68, no a/c. Thats with a stock 3.42 rear. With the 3.90s, it's dropped back down to like 28mpg. I'm kind of surprised going from 3.42s to 3.90s made that dramatic of a difference on the freeway, but it has. City is about the same as before (17mpg).