Posts so far have been my experience, too.
When I ordered my F-250 gasser, the larger 38 gal (?) tank was one of the reasons that I got the std cab 8 ft bed model.
On long trips, even with the larger tank, I don't like getting much lower than 1/2 tank, especially the first time I'm on a new route.
And I've re-discovered Rest-Areas and for taking breaks while towing, no wasted time. I can park, use the bath-room, stretch my legs, do a 'walk-around' the truck and trailer much better than I can at Flying J, Loves, ect.
I am seriously thinking about carrying extra gas on my next trip and either 'top-off' while taking a Rest Area break or drive further between stops at the pump and still have a 'respectful' reserve. I should add that my new trailer is a boat and I will already have portable gas tanks with me. (Need to update my signature)
Fred