What kind of fuel economy are you getting now is the question I would ask? Maybe there's something amiss that can be improved to help your economy (tune-up, repairs, etc). Mine averaged out (hand-calculated over 2 months), I-5/Auto trans, ..same pump fill-up comes out to 17.2 mpg. That's "Average" because average between tankfulls is what really counts. A lot of guys throw out the best mpg they ever got downhill on a windy day. But Average the way you drive, is what matters, and mine is a mix of probably 70% hwy, the rest town and local driving. 17.2 I think is pretty good given the H3's weight & friction. It's mostly flat land driving around here and I don't drive like a maniac (most of the time..ha ha). What's your Average MPG per tankful and how do you drive?
The H3 is about 5,000 lbs with fuel and you riding inside. It's shaped like a sharp-edged bread box rolling down the road on big tires. If your rig is well-tuned there isn't a whole lot you're going to do to "magically" gain fuel economy, other than possibly tires. Get rid of off-road tires if you have them. For reference, my full-sized pickup/s, H3 and a Jeep Grand Cherokee...they all get the same basic fuel economy (averaged out by hand over a couple months). We had at one time two Jeep Grand Cherokee's one with a V8 the other with the 4.0L I-6. The I-6 GC achieved .5 mpg more. My neighbor had the same vehicle with a V8 and his got the same as ours. It isn't uncommon. The vehicles are the same mass. And get this: My older late 80's GM truck and much newer Dodge truck which seems 25% larger, both tk's get the same fuel economy! Both in the 16.5 mpg range (averaged out) range. I have a VW TDI that averages 40mpg virtually every tankful (the way/places I drive). My brother's TDI (manual trans) gets 43mpg. I've rented hybrid cars which got over 50mpg. If you watch Youtube videos you'll see where guys with new Broncos with the off-road pkg ...the larger tires are getting 10-12-13mpg average. Jeep Rubicons don't get very good MPG either. Smaller engines, narrower cabin. But it all comes down to weight/friction/efficiency. None of which you can do a whole lot about except lowering tire friction and making sure it's running top shape. If yours has larger 33"-35" 10-ply or knobby (or big lug) tires, get something smaller & more streetable. That might get you 1-2mpg. There's a guy on the Ram forum who said every mod he made to his pickup cost him at least 1mpg, sometimes 2mpg..till he was down to about 10mpg! LOL
Consider getting a VW TDI or newer (smaller) gasoline car, or EV, and drive the H3 for fun times.
