Absolutely, full auto are available in 500 hp configurations. But the price is huge, I believe you are looking at $30,000 plus more for full auto and $20,000 plus more for a auto shift. (I maybe low on that)
And if you go with a used truck don't get any ideas of swapping for a auto or auto shift. There is one auto you can swap into a used truck without overdrive and that is the Allison-740. But this is a rough shifting auto and will most definitely lower your top speed. And Allison won't touch you with a ten foot pole when looking at a auto shift for a used truck.
I was really worried that shifting was going to be a major pain in the rear and that I would be really unhappy having to shift. (specially a 10 speed) But it really turns out to be no problem and with a upcoming trip to Florida, I really look forward to perfecting my down shifts in the lower range and to get a better idea of what gear to slip into at what speed.
2003 28' Show Hauler Motorhome on a 1995 FL 120
www.showhauler.com