Howdy All,
Regardless of transmission type, "IF" you need to use your service brakes to slow down while descending a steep grade, use the method professional truckers use; use enough pressure on your brake pedal to drop 5mph in 3 seconds then let up, repeat as needed. The trick is to NOT getting going to fast to begin with, start out slow from the top and be in control all the way down without burning up your brakes. If you don't have some type of exhaust brake, GET ONE, its the best money you'll ever spend.