I am so tired of hearing "diesels have little to no engine breaking". I'm a native of NC mountains and diesels have plenty of engine breaking.
The rule of thumb is go down the mountain a gear lower than the gear you came up it in. So if you had to use 3rd to climb it, use 2nd to go down it.
Stab the breaks instead of riding them to slow down.
Pick a speed (let's say 35mph). Stab the brakes until you hit 30mph then let your speed gradually climb to 35mph then stab the brakes again back down to 30mph. If you have to do this more than once every 7 sec or so, gear down again.
IGNORE THE PEOPLE BEHIND YOU! Truth be known, half of them are probably glad you are going that slow so they can hang their cameras out the window.
Hurry the leaves are already changing at higher elevations!