Depends on the slope, I was raised in Colo and grew up driving them. First keep your speed down, you should be going down the same speed you would be going up. Going downhill, first shift into the tow/haul mode.
This will prevent the transmission from going into O/D.
I prefer to downshift to the appropriate gear to maintain the speed I want,
And make sure you are not riding the brakes, they will get hot fast. If you find yourself braking too much, shift to a lower gear.
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