First, i noticed the rendering speed is much faster for 2D textures.
Second, the 2D textures are all translucent. No changes to my code.
They are all drawn using AddQuad:
Rectangle rectangle = new Rectangle( newX, newY, newXsize, newYsize );
renderer.AddQuad( rectangle, new Rectangle( 0, 0, 1, 1 ), index );
Any ideas what could be the issue?