Before you change the sights have some other people shoot it - or better yet shoot it from a rest.. Low and to the left is pretty a pretty common shooter error to have with .45. If you're unconsciously squeezing the gun a little harder as you pull the trigger in anticipation of the recoil you'll get groups that are low and to the left.
I had exactly the same issue with my 1911. I wound up having to do a lot of practice with longer DA triggers (and a whole lot of dry firing) to get over it. Something about the super short trigger travel seemed to make it harder for me to get over that particular issue.
si vis pacem para bellum