As far as shooting low is concerned some of the problem could be that you are used to Glocks w/ a much different grip angle. The Glock grip angles back much more at the bottom of the grip so, if you hold the M&P the same as the Glock, the M&P barrel will be pointing lower. Of course you move it upward when aligning the sights, but during recoil the gun will move differently in your hand than the Glock does.