2 times where the slide did not return all the way forward, with a slight tap it slid the rest of the way forward. could just need a little breaking in.
I know you didn't ask, but you might want to reconsider your solution to your problem. Extra power firing pin springs aren't just for liability reasons. They're a legitimate (and in my opinion necessary) safety feature to reduce chance of discharges if the gun is dropped and it happens to land on its muzzle.
If you need a harder hit on the primer, you should consider a strong mainspring. That's the spring that stores energy for the hammer itself.
You may also have a dirty or rough firing pin channel.