You should make it so the player cannot grab the ledge while the down key is pressed. otherwise he quickly grabs and the lets go.
Also, I noticed when falling down the chamber in the beginning, if you hold the arrow key in the direction of the opposite side of the ledge your hanging on, and then press the jump key, the play moves so fast he hits the wall and shoots upward.
Ex. Player is hanging on ledge on the left side. I press and hold right arrow key then press jump. player will fly to the right, hit the wall, then shoot upward.