Here's a link to the Ford Fleet site and the trailer towing guides. They go back to 2002 so you should be able to find exactly what you're looking for.

https://www.fleet.ford.com/showroom/...ng/default.asp

For ratings on the 6.0, you'll need to look at the 2003-2007 towing guides and for the 6.4, look at the 2008-2010.