It’s been my personal experience that Diamonds are not as consistent as GC’s in different rooms/parts of the country. I have played on them in Colorado, Mississippi, New Jersey, Pennsylvania, Indiana, Virginia, and Georgia. Sometimes they play close to a GC, and sometimes they play like pinball machines. I personally think it’s something about the cushion material, and it is more susceptible to environmental factors than super speed cushions.
I recall even at the same place (DCC), one year it was snowing and they were closer to pinball machines. The last year I went 2 years ago it was warm outside, and they played like GC’s.
So, I’d bet there is nothing wrong with your table. It’s just the normal variations due to environmental conditions.
Also, plus one for template racks, new balls, and a polisher. New balls will definitely bounce more off of the rails. I experienced that myself on my home table.
I completely agree about the blue labels, even in the same pool hall. The Diamond ProAm at the Rack bank different than the professionals which surprised me.