That sounds bad ass. I have been wanting to put one in for some time now but they don't recommend it for towing.
My flatbed trailer weighs 9100 empty and although I haven't weighed it Im sure my F550 weighs all of 10k or more. Figure CC 4wd steel flatbed. All that puts me close to their limit empty.
It would be awesome to be able to split the gears in my 4r100 especially considering my 4 88 gears