Its recommendations include things you might not have considered:
Tire Tread
Fuel economy is approximately six percent better when using tires that have a 50-percent tread depth than if you're using new tires (100-percent tread depth). So those brand-new knobby off-road tires will cost a little in fuel mileage from the increase in rolling resistance and from the additional mass.
Aerodynamics
Full aerodynamic aids can improve economy by approximately 15-percent at speeds above 50 mph. A smaller trailer gap also is more efficient. Aim for less than 30 inches.
Winter
Higher-density air, crosswinds and head winds, more idle time, blended fuel (lower BTU), snow, and more driveline drag are some of the things you face when driving in winter. They can cause a decrease in fuel economy of eight to 15 percent compared with summer. If you want to see how driving in the cold season affects your truck's fuel economy, also factor in prevailing winds. North-south routes have less head and side winds than east-west routes.
Speed
A simple rule of thumb: You'll lose 0.1 mpg for every mile per hour above 55. This equation is based on aerodynamic drag.
Idle Time
Engines use 0.5 gallon of fuel per hour at 650 rpm and 1.0 gallon per hour at 1000 rpm. The biggest difference, of course, is that you get zero-mpg fuel economy when idling, and the more time the truck is at idle, the worse the overall fuel economy. Reducing idle time from 50 percent to 25 percent can improve mpg two to four percent, up to 10 percent overall. Another part of this is the type of fuel your truck burns. Diesels idle at mixtures from 50:1 to 100:1. Gasoline engines have to idle at better than 14.7:1, so a gas engine will use a lot more fuel at idle than a diesel of equivalent size.
Driver Variability
There can be up to a 30-percent difference between a driver who's focused on getting good mileage and one who isn't.
Other Factors
Also realize other things can affect fuel economy, such as the aerodynamic effects of trailers and side winds and engine and driveline-fluid temperatures. The document on the Cummins site covers them all.
Electronic Tuneup
The basic rule has always been that the first step toward a more efficient vehicle is a tuneup (replacing the air cleaner, spark plugs, and wires, changing the oil, and checking tire pressures). But what can you do after that? Consider tuning up the truck's computer.