Current truck: 2021 F350 SRW 7.3L 4.30, standard bed
Current RV: 40ft fifth wheel toy hauler, around 17k pounds
Full-time RV life, I've towed from Texas to Florida to Maine to Colorado to San Diego. I've crossed a couple of 10k mountain passes. The 7.3L can do it all, except pass a gas station.
After 75k miles, about half of those towing, I'm thinking about trading for a new PowerStroke. I see rumors of a new, larger diesel, but if the 7.3L was good enough, then I can't see needing to go bigger than the current engine. HO seems like overkill, though you can try talking me into it. The current 6.7 gets me the power I need, the range I want, and the ability to fill up in the truck lanes on longer trips. I've gotten good at finding Flying Js and other trailer-friendly gas pumps, but there just aren't enough of them.
I originally avoided buying a diesel because I'm unfamiliar with them and I didn't want to be stuck with a problem I don't understand in an unfamiliar place and having to find a diesel tech. It's much easier to find someone to work on a gas engine.
The alternative is to stick with a 7.3L and have an aftermarket fuel tank installed. 58 gallons gets me around 400 miles, 2x my current, which would help a lot. However, at that point I'm maybe $5k shy from the Powerstroke cost and I still can't fill up in the truck lanes if I do want to do a longer trip.
I have nothing but love for the 7.3, its fun to drive and problem free so far. Most people towing under 12k should be looking to the 7.3 first, especially if they tow recreationally, but I think I'm outgrowing it.
The biggest thing I'll miss is Velocity Blue.