Animation for Sprint not Working -Holding Sprint -Releasing Sprint?

Here is my script:

UserInputService = game:GetService("UserInputService")
player = game:GetService("Players").LocalPlayer
character = player.Character
ReleasedShift = true
if not character or not character.Parent then
    character = player.CharacterAdded:Wait()
end
humanoid = character:WaitForChild("Humanoid")
sprintAnimation = Instance.new("Animation")
sprintAnimation.AnimationId = "rbxassetid://5260675637"
sprintAnimation = humanoid:LoadAnimation(sprintAnimation)
sprintAnimationHold = Instance.new("Animation")
sprintAnimationHold.AnimationId = "rbxassetid://5263793326"
sprintAnimationHold = humanoid:LoadAnimation(sprintAnimationHold)
Equipped = false
script.Parent.Equipped:Connect(function()
    Equipped = true
end)
script.Parent.Unequipped:Connect(function()
    Equipped = false
end)
UserInputService.InputBegan:Connect(function(key)
    if key.KeyCode == Enum.KeyCode.LeftShift then
        if Equipped then
            sprintAnimation:Play()
            sprintAnimation.Stopped:Wait()
            if not ReleasedShift then
                sprintAnimationHold.Looped = true
                sprintAnimationHold:Play()
            end
        end
    end
end)
UserInputService.InputEnded:Connect(function(key)
    if key.KeyCode == Enum.KeyCode.LeftShift then
        if Equipped then
            sprintAnimation.Stopped:Wait()
            sprintAnimationHold.Looped = false
            ReleasedShift = false
            sprintAnimation:AdjustSpeed(-1)
            sprintAnimation:Play()
            sprintAnimation.Stopped:Wait()
            sprintAnimation:AdjustSpeed(1)
        end
    end 
end)

It basically makes the player have a gun-run animation. Though it doesn't really work. This is in a local script. If you could try putting this in your own tool for testing that would be great. Thanks. Please fix :D