Well I didn't read all the posts but living in Canada with our larger gallon(160 ounces) I have on every trip on the highway got at least 25 mpg. I have hit 29 a couple times but that is ideal conditions. Warm summer, summer fuel, no wind, and driving by foot @ anything under 65mph. I believe that using cruise on any road that is not perfectly flat will be harder on your fuel mileage.
I will say though that the overhead comp. is pretty close. Time and time again I hand cal. and then convert the U.S. miles/gallon to Imp. and its usually within 1mpg + or -.

 

not sure how good this mpg is but here it goes. I have a short box so I have the smaller tank and I have larger tires(285/75/16) that is why I am not sure what my mpg is but I went from stephenville, tx down to Baytown, tx which is 300 miles +/- a few(according to gps) one way and only used half a tank coming back I was one eighth above half a tank cruise set at 68 mph. I thought it was great

 

Between 5 and 7MPG.

 

I-80 east from Rock Springs Cheyenne WY, tail wind and about 70 MPH I got 23.9 MPG. On east to Cedar Rapids IA I averaged about 21 going 75ish. (empty) Coming back towing a loaded Uhaul trailer and the bed loaded I averaged 16 running 75-80. I have a friend who regularly gets 25 MPG but never gets above 60 MPH. When riding with him I'm always wanting to help him push on the skinny pedal.

 

yea, all true just make sure you stay in the far right lane.

 

That milage is definitely not possible with the third generation trucks, especially newer than model year 2004.5 and newer. Model year 2003 - 2004 see 19 to 20 best (Two injection events per cycle) and trucks after that not better than 14 -17 (Three injection events per engine cycle).

 

I have a 07.5 with deleted smog components. Its a 3500 Mega Cab custom long bed auto. My average now on the highway is 18.8 with cruise set at 68 mph. At 65 it creeps above 19 to 19.2...hand calculated. When I am in the 55-60 range running from Calgary AB to Pendleton OR...my very best was 22.8 mpg...USA MPG. I log 8-10K miles per month so my numbers are fairly accurate.
Towing I can get an average of 12.8 with an all time high of 14.6 and my lowest with the smog stuff gone was 9.6 with strong winds, high profile 12,800 pound 5th wheel and speed was 60 mpg range. Looking back at my pre smog surgery...I was getting 16 empty and as low as 6-6.3 towing. I run all six tires at 80 psi. Not sure what I can do to improve it more other then some electronics to get rid of the last injection event and maybe alter injection timing and duration.

Scotty
p.s. Fee wheeling front hubs is supposed to net some mpg too but I think its over $2K to do that BOMB.
Maybe if I run with the rotation of the planet and the jet stream I can improve it more.

 

That's what I was thinking. I got 25 mpg once between Barstow and Las Vegas. Even though there's some good grade uphills and flats, I think the overall elevations decreases between the two cities.

 

Of course it's possible for 3rd gens to get great MPG. It seems some trucks do better than others.

In fact, 20+ MPG is very possible with any diesel truck (the old 6.9 Fords were easy on fuel). I guess it's luck of the draw. A friend of mine has a 2004.5 and has never gone over 16 MPG.

 

26 is the best I can get with the cruise set on a long trip. Most of the time its around 19. Still not bad. People have a hard time believing 26, but there are people out there (Diesel Power mag) that have done much better.

 

It has a lot to do with the rearend ratio also. 3:55 will absolutely do better than a 4:10. Manual versus auto is better. I have a 2006 3500 4x4 sixspeed and on the road at 60 to 65 is 23 on the computer and in town it shows 26 to 27 but in all cases that isn't the actual milage. you have to figure it milage and fuel used.

 

I get around 24 hand calculated going 1800 RPM over the road.

 

I've gotten 23 with the wind at my back from Albuquerque to Santa Rosa on I-40. But coming from Santa Rosa with the wind in my face it more like 17ish.

 

I was driving east on I-80 in WY a couple years ago in the gasser RAM 1500 (5.2 5sp/3.54) doing about 65 and gradully slowing when I realized my right foot WAS ON THE FLOOR.

That's what wind resistance will do for ya.

 

i get 18 all day long and often 19 driving it easy.

hand calculated, speedo gps adjusted with smarty