Tranny / gear suggestions

[Jerebus67]

Ok it is november in IL and I am looking for a winter project for my Convert.
I dont want to spend a ton but looking for suggestions. I have a ZZ4 crate with a stock 350 turbo and 3.08 gears (stock rearend). I have a Demon 650 ZZ4 carb (not a fan) on it and it is pretty much a dog off the line. The interstate is a good time but wondered what you guys might suggest. I like the mileage I get on the interstate but wondered with a different tranny and some 3.73's could I get the same mileage? I drive it quite a bit in the summer.