Hmm... well, alpha-blending should be disabled given that you have AlphaBlendEnable = FALSE in your shader.
But just for kicks, can you add this next to the line where you set the DepthStencilState:
XNAGame.Instance.GraphicsDevice.BlendState = BlendState.Opaque;
Edit, it has to be something in the Render Target. As I disabled it, and just drew the image as I would any other model, and it worked. But this does not solve my problem, as it still jitters when I move in game. I still need to use a Render Target.
Any ideas why?