Do you run the k_u = gamepad code after the keyboard code, always? Because then you'll overwrite the keyboard values with the gamepad values (a variable can only have one value at a time)
If you want to support using both a keyboard and a gamepad at once, try OR'ing them together:
k_u = keyboard_check(global.input_key[input_U]) || gamepad_button_check(global.active_gamepad,global.input_pad[input_U])