I also bought a new Shield + PC ported and I had similar experience with mine the first time I took it to the range.
The trigger on mine is much better than my original gen 1 Shield.
It's probably the second best striker trigger I have now. My Q5 is still heads and shoulders above the new Shield but it should be.
I can't get the 13 round in the magazine either, I only tried once. When your used to only 7 rounds total in the gun 12+1 seems like a high capacity gun, even if it isn't.
There is another thread floating around here where the Shield plus owner bought parts from Mag Guts and put in his magazines and got 14 in it.
That would be an option to get the 13 round in the mag if it bothers you that much. It doesn't bother me except for the false advertising.
I really like my new Shield and the only thing I could do without on it is the ported barrel.
It makes a mess inside the gun to have to clean up. A tooth brush takes care of it though. The follow up shot is a lot faster with it than without the porting.