Some of the rules that apply to gas engines don't apply as well to diesels. Gas engines are most efficient at high throttle (accelerating briskly) in part because closing the throttle plate and generating vacuum robs power and efficiency from the engine. While some do, many diesel engines don't have throttle plates, and a better rule to follow is just to keep RPM down.
You might want to check this thread out:
http://ecomodder.com/forum/showthrea...kup-21766.html