I get about 18 mpg with my usual driving habits (lots and lots of driving in the Texas "hill" country and to/from Dallas from west of Austin.) This is in a 2012 Ram 1500
with a 6-speed trans, 4X4 crew-cab, small V8 (4.7L) and 3.92 rear end.
This truck was originally spec'd out for a fleet-buyer for work-crews to use around the DFW area, (super-duty cooling pkgs, skid-plate-protection for construction-sites, dual locking axles, towing-pkg, Ramboxes, cargo-protection and extra-tool-storage built-ins, H.D. flooring, higher-output alternator/electric and lighting, etc.) but I'm guessing he didn't savor the idea of workers "hot-rodding" around with a Hemi so he ordered the smaller V8...an engine I actually preferred at the time anyway,... however he took delivery of only a portion of the original order, therefore leaving the dealer with an attractively-priced, well-equipped "left-over" ... which seemed perfect for my planned use....daily driver for a year, then retirement on a ranch, visits with grandkids piled-in a crew-cab, and with only occasional, light towing. The popular Hemi-engine would be overkill for my tastes...or so I thought at the time. And I prefer gasoline over diesel for similar reason.
Having acquired the truck I liked, I then set about to customize it in small ways that further met my needs/preferences. These small changes cannot be simply "ordered" in a replacement-vehicle...they consist of truly personalized things that cause me to be "in love" with my current truck. Buying a completely different truck would require I perform all these little tricks over again, and I hate that thought.
Then along came a decision to get an Airstream a year later, and we've now taken 8 trips with it,...several short ones of a few hundred miles, and two longer ones of a couple thousand, one along the coast and the other up thru the mid-west hills. This has shown me that this engine is fine for level and gentle-hills Interstate, but marginal for the mountains.
I am not someone who is in the habit of changing vehicles every other year. I drive 'em until they're either totally worn-out or they're wrecked, ....so I'll keep it awhile longer in the hopes it can do the job,...but I'm wondering about our plans to drag the AS out West and Northwest. We'll have to see.
Anyway... the thought I'd like to contribute is for those who've discovered their differential gearing is less-than-optimal. When I was in my young twenties I worked for a while for Houston-area Toyota dealerships as an engine and rear-axle specialist. This provokes me to encourage those who don't like their rear axles to don't think they've got to throw the baby out with the bath-water. For a few hundred dollars you can have a reputable shop change your pinion/ring gearing to one more appropriate for towing.
For towing, a rear axle ratio anywhere in the range of 3.92 towards 4.10 or 4.30 would likely make you a happy person, and that change can be done for less than $400. For those who've found themselves owning a non-locking rear axle, for a $1K you can change out the entire setup, and keep the rest of the vehicle you might already favor.
Unfortunately for me, I've got the right rear axle... I just might not have the right engine, which is not as simple, nor as inexpensive a change-out as it would have been back in the good-ol' Hot-Rod days, now that everything is so computerized. I'm hoping our first trips out-west don't end up with me disappointed in the truck I've so lovingly personalized.
BTW, this truck gives me 18 mpg generally, and about 12 mpg when towing the 'stream, most of the time around 65 mph. I'm OK with that.
Hope the comments are helpful.