Duramax Fuel Economy

When I'm cruising down the interstate, what is the best engine rpm for best fuel economy assuming level roads & little or no load in the truck?
Does your recommendation change if the truck is heavily loaded?
Thanks Craig
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I consistently get 22 mpg at 65 - 70 mph freeway driving which tachs out about 2000 rpm. Pulling a 7000 lb trailer I get 16 mpg driving 1/2 mountains and 1/2 flat land. Tach is all over the place when in tow/haul and in the mountains and again around 2000 rpm on the flats. I've got a '04 LB7. Check out http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi if you haven't already, a bunch of great guys and more info than you could ever want. Paul

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