Wasn't there a guy who posted on TDS about messing around with gearing alot for the mileage. i'm wanting to say he got down(or up) to a 3.08 or something around there? I'd probably just try to find something in the 3.50 range. that should get your rpm down around 1700 (guessing) at highway speeds, which would still be high enough for the truck to not be lugging trying to keep up.