Not a Ford, but a 15 Ram with the 6.4 Hemi and Auto. Previous truck was a 2004 Dodge with 5.9 and Manual transmission. Both hauling the same Lance 815 which weighs 2,400# loaded for a trip.
I run about 64 interstate and 57 backroads. On mostly flat highways, she holds 6th gear at ~1600 rpm which is actually lower than the Dodge did due to double overdrive. She will shift going up hills, but usually only 1 gear to overdrive at about 2k rpm. Worst case is on a 6% grade for 3 miles, she will get down to 3rd gear at about 3,300 rpm but will hold the 64 mph and doesn't sound like she's will handle it all day long. After 19k miles with the camper, hand calc is 12.4 mpg.
My father with his new diesel DRW hauling a 5k TC is only getting about 11.5mpg because he uses tow/haul mode because of how it improves the exhaust brake usage. But he didn't have a choice since he also has a 16k FW which required the extra torque.
I also have a 2,800# boat I tow behind on occasion and she handles the extra load with no problem. She will maintain 6th gear without bogging but only if I run 62 which I don't like to do. So I drop down to 5th gear and reduce my speed to 57mph which is about 1700 rpm and she handles it fine. With the boat my mileage drops to about 11mpg.
I track all fuel mileage in both trucks so have a good baseline comparison. If I had kept the 04 vice the 15, I would have only saved about $400 in fuel cost over the 45k miles I've driven the truck. Diesel in most places I travel is a 10-15% premium.
Yes, sometimes I miss the torque of the diesel. Yes, I mostly miss the exhaust brake of the diesel. But it wasn't worth the risk of the added repair expenses of the complicated diesel emissions nor the upfront cost.
If I suddenly had to replace the truck tomorrow, I would go gas again without hesitation.