Originally Posted by SteveSueMac
I have the same exact truck. Avg 15.2 mpg over 40k miles, at least half of that trailering. How the heck are you getting 22.5 unhitched????
(Time killing this morning)
Record-keeping is usually spotty. Someone using an app like Fuelly or a paper log of all fuel burned is the better source.
To make comparisons about mpg, one must, in order of importance, find:
Details of truck specification (not just 4WD versus 2WD, SRW vs. DRW, or auto versus manual, but tire type and tread design. Aero helpers. Etc)
Driver input (motivation towards fuel economy such as constant use of cruise control; travel set speed; extent of idling, and so forth).
Comparisons are never as simple as they might appear. TT design plus weight and length also apply.
FWIW, I searched extensively when I bought my rig using the above. What I found was that, in the South Central US, with aero aluminum trailers of 28-35' and weighing from about 7-11k lbs, and at speeds under 65-mph, that early HPCR Dodge Cummins were averaging from 14-16/mpg.
This accorded with my experience, overall. I fell within a "normal range", in other words. FE was and is an important consideration for me. Truck spec and truck use.
The weak spots to first consider is ones habits just ahead of truck details. Control for travel speed solo and towing, and things like tire tread design, etc.
In highway solo driving I was at the high end at 24-27/mpg. Where 2WD, SRW and manual trans shone. Travel speed on CC was 58-mph (slower than towing mpg above. I have since changed that). Next to no idle time. Minimization of accel and brake events as well as next to no lane changes. Trip planning and discipline.
So my overall average (50/50 town/country) over the past 55k miles is 21.36. At an average speed of 40-mph (engine run time into miles over a given distance). Towing is now 15-17/mpg in this part of the country.
In short, where, what and whom? (part of country, and at what speed; with how owner spec'd truck). That's the minimum for a comparison.
As a final example: those who have radical changes in travel speed between solo and towing are usually those with the worst fuel economy.
15-mpg annual average is about right for CTD contemporary to mine where 4WD/auto plus tires with open shoulder tread is the norm. From reports across most of the country. I'm an outlier. So would someone living well up into the Rockies. Or northern Alberta. Etc.
SteveSM, what is the percentage drop you're seeing from solo to towing (preferably where truck load is similar)?
40% is the norm for all vehicles, where up to 50% for a gasser pulling a box is that range; and down to --even below -- 30% is possible with a small turbo diesel pulling a smaller A/S.
Test your truck/trailer against the Cat Scale solo weight from when you did WD setup. Approximate the loading with sand, iron or other. A 200-mile loop back to same pump at same filling station. Cruise control, at towing speed.
Think of this as your adjusted highway mpg (as with finding adjusted empty weight being different than published ship weight where driver, full fuel and permanent gear are aboard), as percentage drop is the number that tells the most about the rig and its relationships.
That done, you'll have accounted for problems currently unaddressed, and can then make more accurate comparisons as to something seemingly as simple as solo mpg.
Towing highlights the problems. With turbodiesel pickups (and after tread design) it is CAC system leaks, brake drag, steering slop, and alignment. Second order is engine tune (emissions, usually). Finally are emissions deletes.
A truck with tuning for DEF ought to be seeing 22-mpg at or below 65 given stock tires, ride height, less than a thousand pounds aboard, and lie idle time. Unless GM is truly inferior in this.