I have a 2014 Limited with the four cylinder engine. I have the same issue. I put the Jeep into neutral while going down a steep hill. The reves went way up upon entering "N" and the vehicle sped up considerably. When I engaged the transmission by putting it into "D" the revs went up again dramatically and the vehicle slowed down - all without touching the brakes. I should add the Jeep was going 80 kms/h when I tried this - no other traffic present. The car freewheeled about 1 Km when I engaged "D".In all other cars I've had, the car will accelerate while going down a hill in "D", as if you put in the clutch with a standard transmission. The Jeep doesn't. Neither good or bad thing, I guess it is a Jeep thing.
From Owners manual:
Towing the vehicle, coasting, or driving for any other reason with the transmission in NEUTRAL can cause severe transmission damage.
Most automatic transmissions do not have pumps that cool/lubricate while the trans is in neutral. A few do, like the older Honda CR-V, where it can be moved in neutral below 65 mph and with other provisions. Coasting in neutral with the 9-speed is a big no-no for a number of reasons to include its small form factor and concerns already addressed on this forum about over heating the tranny.
<<I put the Jeep into neutral while going down a steep hill. The reves went way up upon entering "N" and the vehicle sped up considerably.>>
The system is not designed for coasting in neutral. When you put it in neutral, the load was unexpectedly removed from the engine and it revved as a result. The vehicle sped up considerably because it's in neutral. It's called gravity.
<<When I engaged the transmission by putting it into "D" the revs went up again dramatically and the vehicle slowed down - all without touching the brakes.>>
The engine had settled into idle state, and then you engaged the transmission again. The revs went up because the wheels and other parts of the driveline drug it up there. Again, the system is not designed for this. Lord knows what gear it tried to shift into at that speed. Then it slowed down as it should. It's called engine breaking.
It's posts like this that make me wonder if, in some cases (not all), it's the driver that's ruining these transmissions.