I've got a 6.0, but it is a 2002 with the 4spd tranny, so I'm down a couple of gears, and a little HP from the new ones. It has been a very good engine, and still runs great at 213k miles.
I will say pulling my 8k lb TT that I've been down to 30mph in 1st gear in the mountains on 3 different roads. It got up the hill, but we got passed by a dumptruck :).
At 10k, I think a lot would depend on the area you tow in. We have some short steep hills in north GA, NC, and TN. If you are in flatter areas, the 6.0 will be fine. I think at your weight, you are at right at the point where you start to get into diesel territory.
Have you considered the RAM, or Ford gassers? They both have just a little more power than the 6.0, and might be worth a look.
