I think I said it before - when i got my USPc in 9mm, I kept shooting low - At first I thought it was the sights - as I don't do this with other guns. I still had my fullsize USp at the time, and I shot that gun fine.
After a few trios, I shot well with it every OTHER trip. Then, by 800 rounds, I started to get consistent.
I let someone else shoot 1 mag thru it last month - sure enough - he fired all shots low.
For whatever reason, ya gotta "work" at it. Just keep shooting it. It will come.
Granted, I haven't had to do that on my other guns - at least not to this extent. But, just keep shooting w/ it. I have almost 1300 rounds thru mine now.