I originally bought my F250 with the 5.4 for the payload capacity while towing a Work and Play 18EC bumper pull toyhauler. I bought the work and play when I owned a 2004 Toyota Tundra with the 4.6 V8. By going to the F250, I got a lot more payload with a substantially heavier duty truck. I also went from 240hp to 300 hp, so I still improved my engine capability.
I now have a lighter camper, delivery sticker of 4193 pounds, that I could pull with an F150, but I have the F250, and like the solid feel it gives me while towing. But even with this lighter camper,I would rate the 5.4 as adequate. In the flatlands its fine. Pulling it up the hills from Springfield, MO to Branson (30 miles at the most), it has to rev. I wouldn't want to have to pull hills like these all day long. Like I say, its adequate, and the F250 chassis is nice to have.