I am having some issues with my mouse coordinates in XNA - the 0x0 is arbitrarily near (but not in) the top left corner of my screen.
I am running the game in
Your draw call is not offsetting the texture at all. If the "pointer" part of your image isn't in the 0,0 position (top left) of your Texture, the positioning will seem off.
Add a Console.WriteLine(pos);
to your update to see the position it is drawing to. Remember to remove this after your debugging because writeline will kill your performance.
Try one of the overloaded SpriteBatch.Draw() calls which factor in an "origin" which lets you decide which point of the texture should be drawn at the position. In the following code tweak the Vector 2 based upon how your texture is drawn.
batch.Draw(tex, pos, null, Color.White, 0.0f, new Vector2(10, 10), SpriteEffects.None, 0.0f);