Which year/trim of a truck are we talking about here specifically? I’d be interested in not refuelling for months of city driving.

Assuming we’re just talking about driving around for errands and not things you use a truck for, this would still be impressive.

2021 Ford F-350 XLT, long bed + crew cab, diesel engine (do F-350s even come in gas...?).

Family and I used it for moving across state, and with no load (or very light load, no trailer) and a full tank it could make a 700 mile journey in one go with fuel to spare. That included going up a couple mountain passes.

Fully loaded (20ft enclosed trailer and truck bed), it still made about 500 miles of the way before we needed to refuel.

Worth noting, we found the mileage wasn't actually affected in any significant way by any cargo we hauled. It was pulling that trailer, regardless empty or loaded, that reduced mileage (aerodynamic drag!).

Street driving is less efficient than freeway driving, obviously, but with a ~40 gallon fuel tank it should still make stopping at the pump a very infrequent event.

Doesn't change much to your argument. But fuel doesn't last for months sitting in a tank. Gas will absorbs moisture from the mandatory ethanol mix and become quasi useless, and diesel will develop algae, clogging the piping and filters.

Speaking from experience it really isn't as big of a problem as it sounds, and there are additives you can use if it does become a bother.