I bet it has 3.08 axle gears and a good torque converter if it's getting 15 mpg.
I highly doubt he has 3.08's. I've never seen a 3/4 ton axle with them before. Is a 3.08 gear set even available for a 14bsf?
I'll be the voice of the other side. I would ditch the sf and find a 14bff. I don't see a semi floater as an upgrade over a 10 bolt. Just a heavier version.
Martin

I don't know what you would do if an MSD went out in the wilderness. Have a spare box? 