character controller not working

I’m trying to have my character be able to move even if airborne. But when I jump, he only goes up about 0.08 - 0.1 units. Then when he falls back down, it’s as if he is in slow motion, even though I set the gravity to 20. My code is below.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement : MonoBehaviour {

	public float Speed = 6.0f;
	public float JumpSpeed = 8.0f;
	public float Gravity = 20.0f;

	private Vector3 moveDirection =;

	// Update is called once per frame
	void Update () {
		CharacterController controller = GetComponent<CharacterController>();
		moveDirection = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
		moveDirection = transform.TransformDirection(moveDirection);
		moveDirection *= Speed;
		if (Input.GetButton("Jump") && controller.isGrounded){
			moveDirection.y = JumpSpeed;
		moveDirection.y -= Gravity * Time.deltaTime;
		controller.Move(moveDirection * Time.deltaTime);

sometimes gravity is weird, try setting it to something like 1000-500

My character falls normally now @ThePhantomGoat , but the jumping is still weird.