I use my trans for breakng on hills and very seldom have to use brakes. Even went to low range going down some of the 10% grades on the trip to Alaska. Watch the rpm and never shift down if the speed is high. I never excede 4000 rpm on our v10 ford MH automatic transmiission.
I agree with the previous post, except that the max RPM of the V-10 is quite a bit higher than that. The max torque for that engine is 4600 so you are safe to go some above that. But, I also keep my RPM below 4500 by using the brake as needed.
If a down slope is long and you do not use the engine and transmission to hold you back you will likely over heat your brakes and could cause several different problems, any of which could lead to brake failure.
Kirk is correct on the V10 RPM being higher and not damagng the engine. I just try to stay around the 4000 while gearing down. Seems to work pretty well for the load I carry. Did hit the 5 grand a couple of times on the long grades but just don't like to hear the engine scream. Tap the brakes and slow it down. Heated brakes don't work very well and sure don't like the idea of using those truck exscape ramps