I drove a Cornbinder flatbed for a building supply company this summer that had a 5 speed trans and a 2 spd axle, with an inline 6 diesel without a turbo. The guy that taught me to drive it said to do this pattern unless it is absolutely piled high:
1-low
2-low
3-low
4-low
5-low
5-high
Staying in low range helped out driving around in developments, subdivisions, and in the city where the speed limit is 20-35 mph. Once it was out on the open highway, it would go about 55-60 at about 1500 rpm. That keeps you from having to change so many gears.
