How to dispatch mouse movements to other windows without it being laggy

[jacobawesome7]

Hi, so I have this program that makes a transparent window over a game window so I can make a kill-counter. However, because it is over the top of the window, I have to make sure it takes all clicks and mouse movements and sends them to the game window so I can play the actual game. Whenever I move my mouse it does send the message to the game, however the games response to the message is very laggy and is just snapping to other places instead of moving smoothly. Also, I can't even move my head left. I have done a lot of research and tried many things but nothing worked. Thanks in advance for all the help!

Code that sends message to the game window:

   case WM_MOUSEMOVE:
	{
		ShowCursor(false);
		SetForegroundWindow(gameWnd);
		SetCapture(gameWnd);
		SendMessage(gameWnd, message, wParam, lParam);
		return 0;
	}break;