I just did the same move you did - moving from 2005 Duramax to a 2015 F250 6.7L powerstroke.
I do not have the hill decent, but do have the exhaust brake button. I have only had my truck for 1000 miles so I haven't done much testing. I do know that when I connect to the trailer, the truck knows and will change on it's own for towing/braking. The chevy I had, as you did, needed that button on the shifter pushed for tow/haul.
Unlike the chevy, I can use the exhaust brake without the trailer (could do it with the chevy if needed by pushing the tow/haul button, but rarely thought about it or needed it to work that way without the trailer). I don't know if I will ever need it, but that could come in handy when traveling in the mountains.
I agree with the other posters about being able to lock out the upper gears. If this truck is anywhere near the old chevy, that will come in handy. Again, you could do it with the chevy by moving the gear shifter down a gear, but I like the way the Ford has the buttons to make the selection - feels less harmful than shifting down.
For the locking differential stuff, I can't help. I will never use it, and rarely even use the 4x4.