I have a player object that can move and jump. When it starts falling after a jump the fall speed is good. However, when the object falls naturally off a plane and down on a lower one it starts falling very fast. In fact, it reaches about twice the fall speed of a jump even though the jump is is twice as high as the cliff.
Have you played with the drag property of the rigidbody of your falling object? It's basically the air resistance. This might solve your problem.
When you jump lamdsingspeed = jumpspeed. When you fall you fall by default with normal gravity, being Vector3(0,-9.81,0). You can change this by going to Edit > Project Settings > Physics
I just fiddled with the same. What I did is when the CharacterController is grounded. Then I adjust the gravity to (lets say) 2 so when the player falls of a platform he will not fall like a 2 ton rock. Then when the character performs a jump I turned the gravity back to normal so the player dose not go sky high.