How do I get my run animation to play while i'm already walking?

I've been experiencing with my own custom animated sprint script and i'm having problems with the Animation starting when i'm running but not when i'm standing still. here is my method:

local UIS = game:GetService("UserInputService")
local Player = game.Players.LocalPlayer
local isSprinting = false

UIS.InputBegan:Connect(function(input)
	if input.KeyCode == Enum.KeyCode.LeftShift and isSprinting == false then
		isSprinting = true
		Player.Character.Animate.run.RunAnim.AnimationId = "http://www.roblox.com/asset/?id=5202688739"
		Player.Character.Animate.walk.WalkAnim.AnimationId = "http://www.roblox.com/asset/?id=5202688739"
		Player.Character.Humanoid.WalkSpeed = 25
		if input.KeyCode == Enum.KeyCode.W or input.KeyCode == Enum.KeyCode.A or input.KeyCode == Enum.KeyCode.S or input.KeyCode == Enum.KeyCode.D then
			local Track = Instance.new("Animation")
			Track.AnimationId = "rbxassetid://5202688739"
			local Anim = Player.Character.Humanoid:LoadAnimation(Track)
			Anim:Play()
		end		
	end
end)

UIS.InputEnded:Connect(function(input)
	if input.KeyCode == Enum.KeyCode.LeftShift and isSprinting == true then
		isSprinting = false
		Player.Character.Animate.run.RunAnim.AnimationId = "http://www.roblox.com/asset/?id=180426354"
		Player.Character.Animate.walk.WalkAnim.AnimationId = "http://www.roblox.com/asset/?id=180426354"
		Player.Character.Humanoid.WalkSpeed = 16
		if input.KeyCode == Enum.KeyCode.W or input.KeyCode == Enum.KeyCode.A or input.KeyCode == Enum.KeyCode.S or input.KeyCode == Enum.KeyCode.D then
			local Track = Instance.new("Animation")
			Track.AnimationId = "rbxassetid://180426354"
			local Anim = Player.Character.Humanoid:LoadAnimation(Track)
			Anim:Play()
		end		
	end
end)

Make Sure your Animation is actually set to Action, The System goes like this, Core -> Idle -> Movement -> Action, If your Using Animation Editor, Click the Three Dots, Proceed to Animation Priority and Choose Action.