Just did a trip to id. and back. Truck in sig. and 30ft three axel enclosed trailer(8.5 x 30 x 9 tall). 22000#. A little disapointed in mpg but driving was great, took off about 2 1/2 hours off trip each way. Thru Ca. mountains at 55-60mph = 9mpg, nevada at 70-75mph = 9, idaho at 65-70 = 9. just tell it how fast and set the cruz it said ok but 9mpg. 1673 total miles/185.66gals = 9.011. My 1992 ctd 5 speed got about 11, 95 1 ton ford psd 5 speed about 10-11 but both struggled to maintain less than 60 mph average.
Clark

 

Your 92 had less than 200hp. your 95 powerstroke had about 215. now you have 325........the numbers add up about right to me. You could add another 1mpg if you had a manual.

 

Also, I bet if you dropped to 60 in the flats, you'd pick up a couple MPG.

Towing a 30' 5th wheel with an 03 SRW 3500 stick, I could see 12, or slightly higher.

Now, with a taller 40' tripple axle 5th wheel and an 06 dually stick, I get 10.

Duals I'm sure have a MPG penalty, as does the 600 engine vs the 555 HO.

 

I would expect 11+ mpg from mine in that same situation. I have a manual though. Heavy load of tractors from CA to AZ on a big gooseneck still got over 11 mpg. Same with my 5th wheel.

Mine averages over 19 mpg in mixed driving. I think I just got a good one. It's bone stock. I usually run 70+ too, even loaded, so if I slowed it down some, I'd expect even better mpg.

 

try to maintain 1900 rpm as much as possible, this is the key to fuel mileage.
I also like to run with 2 stroke oil in the fuel (.7oz per gallon) and every 4th tank run a full mix of diesel kleen (silver bottle).

 

Just made a short trip to Glendo wy and back. Hand calc came in at 11.4. Cruse control set at 70/2K RPM. I tow a 26Ft toyhauler, not heavy 7K but like pushing a bill board.

 

A couple of years ago, my family took a trip out west to California and back with a small hybrid trailer, ~4K lbs. The total trip was just over 8K mi. I usually got 13-14, except for one stretch in western Texas. Going 80+ mph (speed limit was 80), pulling the trailer, and with the A/C on (it was 105 that day), I got 11 mpg!

 

I pull a similar load with my 07 MANUAL and get 12-13 every time.

 

I tow a 14K high nose Fiver. I've added a few goodies as shown in name. Took a trip from N.O., LA to Winnipeg to Fairbanks to L.A. back to New Orleans, total of 11,542 miles burning 1054 gals. of diesel. Rarely disconnected from trailer and averaged 10.95 mpg. That's an '03 dually HO and auto trans. I'm sort of like one of the other drivers listed in this thread, I like to keep my foot stuck in it. I like to keep tabs on my mileage but rarely travel except for mileage. I usually like to roll on those long hauls. Love that power and torque.

 

Slowing down definitely makes a world of difference. Mountains and hills kill your mileage quickly though. Your numbers are right in line with what I got in my 07 5.9 and my 08 6.7 trucks. My old 03SO got much better and I am hoping this 04 truck does too. No numbers on it yet though......

 

i got 10.38 mpg on a 395 km trip pulling my 10,000lbs 34 foot camper. the overhead said 10 mpg....

 

I pulled my 9000lb travel trailer from SC to AL last weekend running 65 the whole time. I got 12.8 going down and 11.1 coming home. The 12.8 going is probably a little off because I put on about 80 miles not towing while I was there before I filled up. The 11.1 coming home was all towing, but I did run 70 for about 30 miles. The best towing mileage I ever got with this truck and trailer was 13 and it was a mountain trip from SC to TN. The twisty mountain roads would not allow for more than about 55 mph.