Dear Shooter:
This is just a thought. Most right-handed shooters will "pull", "flinch" low and to the left. However, like the other gentlemen said, you will be suprised to see how little the sight needs to be moved to correct this; also, it appears that if you are pulling off you have a very consistent pull!
I'd try moving the sight as suggested and then concentrate on trigger pull - I have NO experience with Glocks, although I use a 10MM Model 20 Glock.
Harry B.