DCP, I don't know if you will find someone towing those weights around so I thought I would comment on my thoughts since I have a 2012 F250 with 4.3 rear.

The way i read the charts, you will not find Ford recommending that you can tow that much comfortably with the 6.2. Recommend you stop in when passing a dealership and grab a brochure and check out the ratings.

On the slush box issue. Check out the features of the Ford new 6 speed automatic. It has been a while since there were really slush boxes on the road. The torque converter locks up early on. Also you can put the trans in "M" which stands for manual and shift it electrically as you please. You can also limit top gears electrically when in drive.