I haven't been on MUD for months but with the price of gas where it is I checked in to see if there was a post about this particular question. Here is my setup and what I am seeing.
- LC Alone. 2021 HE w/ Slee sliders, Gamivitti roof rack and 65/285 KO2s. A single ARB drawer. Weight with me and cargo ~6600#. Seeing ~17.5 on the highway which for me here in Central Oregon is 60-65 MPH.
- Trailer. Full size, 2-axle travel trailer with a GVWR of 5800 and we are just about at the number when loaded. (When towing I have ~750# of tongue weight.). When towing I am getting ~10.5-11.5. The problem is that we often go from Central Oregon over to "the valley" or "the coast" which means going over some minor (compared to the Rockies) mountain ranges. When climbing though the mountains I am seeing ~8.5-9.5.
We are not aggressive drivers at all. Especially when towing I tend to stay closer to 60 than 65 and I accelerate gradually. It helps that we haven't had to do much towing on interstates. Yet.
I tow a 7,000lb surf boat with my 2013 LX and average around 10mpg at 70-75mph. I weighed it over Memorial Day at a Cat scale and combine weight was 13,880. My vehicle is 100% stock.
In Alaska with crappy roads, no real highways, mountains, and curves. I tow a ORV 22BHS (6800 lbs) ~10k miles a summer. ‘13 LX, stock other then 33” tires on 17’s and LC rails. I keep it consistently 5 mph under the speed limit so mostly running 50-60mph. I feel lucky when I get 9mpg. Most of the time I’m ~8.5-8.7 mpg. Last weekend coming back from Seward I had a good 30-40 mph tail wind the last 50 miles and was able to get 9.4 mpg on the 140 miles home. I’ll add that aero (or lack there of matters way more then weight. My brother has an 18’ ORV that is ~3k lighter then mine with a similar front profile, I get pretty much the same mpg when I’ve towed his. Had an AS before the ORV that was a similar size and weight I got more like 8.7-8.9 as it was lower and rounder.