I have a bunch of Glocks, 17's, 19's, and 26's, and they all "shoot left" for me, with the rear sight centered. For me to get POA/POI, I have the right edge of the rear sight on every one of them, on the right edge of the dovetail.
I put night sights on every one I buy, and have the tool, and I know exactly where to put the rear sight that I normally dont have to move them when I first shoot them.
Ive tried all the things the experts say Im supposed to do, change my grip, change my finger positions, etc, and they all still shoot left, if I dont move the rear sight to the right.
Odd thing is, Glocks are the only guns I have to do this with. All my other handguns, auto or revolver, all have the rear sights pretty much centered in the dovetail, if there is one. The Glocks are the only ones I have to change.
I dry fire daily, and the sights are rock solid when the trigger trips and they dont move with the release. The gun shoots POA/POI with the sights as I have them set, and when I point shoot, without the sights, the rounds go where Im looking when I shoot, so figure that out.
I agree 110% with the dry fire thing too. Its a major help, and beneficial for anyone. I use snap caps, and more as an added safety thing than anything else. If you clear the gun, and insert a snap cap in the chamber, you cant have a loaded round in the chamber if you just put a snap cap in there.Cant hurt the gun having it in there either.
Trigger wise, I suppose its up to you. I shoot the factory triggers that the guns come with, and thats for all my guns, not just the Glocks. The biggest advantage there is, they are all the same for the most part, and I dont have to dump more money into any new guns I get, trying to keep things the same.
Personally, I wouldnt get to crazy worrying about all this. Just drift the sight to the right where you need it and move on. As long as you hit what you were aiming at, who cares?