Stress in a log is hard or impossible to overcome. It is amazing how much stress can exist in a seemingly straight log. You could mill another piece, and if it comes out satisfactory, end coat it with a wax sealer. This will help control the drying process. Also, keep the beam out of the sun while you do this. A covered area with some air flow works best. This is a pretty slow process, especially with a cant, or beam of this size.
