Ford 6.2 gas vs 7.3 gas highway gas milage

Reality Check wrote:
We have one 6.2... a 2017 4x ext cab, and although it doesn't carry a camper.... it tows a trailer, 26' box (read...wind resistance) which is approx 6000lbs. It gets about 8.1 avg in the mountains. Obviously better on the flats.

I have opposite experience. When driving big vehicle in the mountains, driving in 40-50 mph range I am getting very good mpg.
Once I hit flat freeway, the speed goes one way and fuel gauge the opposite.
When I was moving from San Francisco area to Vegas, I made 3 trips with cargo trailer. Going from SF to LV loaded I always had way better mpg, than going back empty, even I always kept my CC at 60 mph. It was all in desert winds.

We have a new 2020 6.2l with ten speed tranny. Hard to believe but all reports indicate both the 6.2 and 7.3 are getting very similar mpg.
At the time we purchased our truck the 7.3 were very limited in inventory. Don’t know what the supply looks like now.
In any case the 6.2 has been great for us-no complaints.
We haul a 4500# TC or tow up to 12,000#. No problems at all. Very pleased with this truck.
Bill

Edit; I realized I didn’t answer your question. An average weekend trip for us with the TC is ~500 miles. Fuel consumption is ~ 11 mpg. Pretty much what I was getting with the previous diesel. Love the 48 gal tank in this truck. I filled up yesterday and (without TC) have a projected range of > 600 miles.
We have now completed our first full season of hauling the TC or towing the Airstream to all of our usual haunts. Very happy with this truck and the decision to go with gas.

We have one 6.2... a 2017 4x ext cab, and although it doesn't carry a camper.... it tows a trailer, 26' box (read...wind resistance) which is approx 6000lbs. It gets about 8.1 avg in the mountains. Obviously better on the flats.

I think for real life comparison fuelly.com is the best site, even you will find some reports that are way off the line.
But standard procedure for comparing statistics - you ignore the high and low extremes.
The 7.3l owners report between 10.8 and 12.4 mpg
6.2l reports 9.6 to 12.4mpg
7.3 l is newer engine and expected to have better fuel management.
The above numbers are without explanation what load, so most likely empty truck.
Big camper will cut down 30-40%
We can split hair here, but reading the statistics - the higher mpg are reported by owners with just few fill ups, when those with 30-50 fill ups have it going down.
I would interpret that that new owners drive carefully for some time and lower speeds bring higher mpg. Once they start putting miles on it, they start pushing it and mpg drops.
It is also common that new truck is used for grocery getter and showing off, when aged trucks are getting beaten up with hauling and towing.

According to real world MPG from owners the 7.3 is getting better mpg. I was surprised to see that.

https://www.ford-trucks.com/forums/1614398-updated-7-3-mpg-8.html#post19663873

general comment
You should know that weight differences with different load plays minimal role in highway mpg. They do on city driving.
What matters a lot in highway/freeway driving is frontal area and aerodynamics.
Than last comment about gas engine mpg
"if you have to ask, you can't afford it"