Big long gun (for a 9mm) with a big long, heavy slide, and a big, hard recoil spring.
You will need to cycle a few hundred rounds and try some 125gr NATO, +P, or 147gr subsonic.
Mine stovepiped a round or two initially and you could tell it wasn't able to cycle the slide all the way because the last round wouldn't lock the slide back.
This is normal. My brand new P30L and P30 did this.
Don't send it in because the next one will do the same.