My dodge will engine brake if I use the cruise control. Down near the bottom (or far side) of your shifter you should have a low gear that isn’t first. You can shift into it under 50 and let off the gas, your car should slow down. Test it’s rpm range on some flat ground first by accelerating to around 50… On the mountain is not where you want to first try it.
At minimum, shift out of overdrive into regular drive.
I’ve also read The book of the damned by Charles Fort.