I suppose individual perceptions may vary, but “stacking” isn’t a word that comes up often when discussing Beretta triggers. I certainly don’t notice it on any of my 92’s.
Is there a way you can find another 92 to compare, or perhaps someone experienced with 92’s to try out your gun?
Mechanically, I’d check to see if the trigger bar is rubbing the stock panel. If that’s not the cause, I’d look into the possibility of the hammer strut is rubbing or binding somehow, either on the spring coils, or the hammer/strut interface, and ensure the trigger isn’t binding on the frame.
That’s all the possibilities I can think of at the moment.
ETA: Also make sure the firing pin block moves freely, since it lifts near the end of the trigger stroke.