I've read numerous threads where guys say they are getting 22 mpg unloaded running 75+ mph and 15-16 or so at 65 mph pulling 10-12K trailers. What's up here?

My truck is an 01 2500 4x4 qcsb Auto 3.54 gears (sig is wrong). Only mods are an Edge EZ, 4" exhaust, ARE air filter and 305/70 Silent Armour tires. If I stay under 70 mph I get 19-19.5 when all highway. Average city/highway is around 15. When I haul my 13K 5ver my mileage is around 10-12. My mileage amounts are not taken from the overhead. Though I have calculated the difference and found it to be off 1-1.5 mpg.

So, who is off?

 

I have thought about it and concluded that the differences must be from the driving style and to a smaller degree from the mods. My truck is stock, with a manual tranny (better mileage), and I drive it at 1700-2000 rpm all the time on the highway. Never get it to 2500 rpm. My mileage is 18.5 daily driving and was above 23 on a long highway trip, keeping rpms at about 1800. I do not floor her on hills to "feel the push", I know it will do it but I baby it. I let the truck coast on hills if it is safe and not excessively steep. I never saw black smoke the way I drive, and I see other diesels smoke all the time. It is the right foot, how much you play with the gas pedal, I think.

 

Many of the higher MPG trucks are using a good set of injectors and turbo charging that helps reduce drive pressure.

Dave

 

I get approx 1mpg better than you and all I've done was new injectors (better or cleaner spray pattern), new IAT sensor, that's it.
I will add a fueling box soon to get extra mpg, but I am looking at best mileage not best hp or smoke possible.
My driving style is not very careful at all but mainly it's highway and interstate, I don't live in the city.

You have to compensate your tire size for your mileage.
Get/borrow a GPS and calculate again.