Our tester had the Electronic Shift On the Fly (ESOF) option, but the hubs can be manually locked to override the automatic control. Ford recommends they be kept in AUTO mode for best fuel economy. It's true! Ours came locked, but we switched to AUTO and picked up about 1 MPG. Overcoming all that friction from the engaged gears and clutches eats up the fuel.
Read more: 2008 F-250 Super Duty 4X4 Diesel test drive and review
Read more: 2008 F-250 Super Duty 4X4 Diesel test drive and review