Sounds like two separate problems. 1. Holding the arm in position. 2. The arm not having enough power to go up, and then moving down too fast.
1. If you are coming from Vex IQ, then you are probably looking for a "Hold Position" setting for the EDR motors. Sorry, but that capability is not built into the EDR motors. That's one of the reasons why the IQ motors are called Smart Motors. In EDR you will have to write the code that moves the arm motor to exactly the position you want (without bouncing back and forth), and then keep checking the position of the arm, and adjusting it if it starts to move down.
2. Make sure you have your gear ratio for your arm configured for power, as opposed to speed. If it is geared for speed it won't have enough power to move fast on the way up (and might not make it up at all), but it will have power and speed to go down. To be geared for power, you should have a small gear on the shaft coming out of the motor, and that gear should mesh with a much larger gear that actually turns the arm. The right gear ratio will depend on the weight of your arm and what it is carrying. A good place to start is using the smallest gear available on the motor shaft, and the largest available gear connected to the arm.
Hope that helps