Vex V5 motor regulator

Hello, recently my team has received the new V5 items. However I have a couple of questions regarding the motors. When using the joystick controls diagonally into the bottom left corner the motors run at full speed. But when I use the buttons or any other joystick rotations the motors run very slowly. Then I looked at the motor set up and it said that the motor regulator was set at 18. So I was wondering if there is something I can do to always make the motors run at full speed. Then when I say very slow I mean the velocity is only at 50%.Another issue that I am experiencing is no matter what speed it is on the motor is going fats then slow fast then slow in short spurts of time.