I am getting ready to replace my C4 trans with a brand spanking new T-5z. With the gas prices now, it got me thinking what kind of gas mileage I could expect to get. I am getting 13/15 MPG with the C4, 3.50 gears, and a warmed up 289. A lot of you have changed to OD; I would appreciate it if you could let me know what you get. Thanks,