Might be worth a new thread.
My 19.5 also had a hitch from the factory. Out of the box it felt great, then after 500-1k rounds it started getting worse.
It almost had a double rolling break. The weight would build, then go down, then hit the actual "wall" and break. Adding a minus connector reduced the second/final break which almost made it feel worse. It also added more travel between the first and second break.
Eventually it drove me to get the GPT. After ditching the GPT I did some tinkering to figure out what was happening. For my gun the root cause is the trigger bar on the firing pin block.
Viewing through the magwell I could see the trigger bar start on a normal path but during the pull would move laterally outward before hitting the frame and slide. That lateral movement/twist was my first "wall". The trigger bar wouldn't begin to depress the safety until all of the lateral movement was done. When the safety was fully depressed the trigger weight would be substantially reduced before the final wall.
I ended up polishing and radiusing the firing pin safety. I also swapped the spring for a reduced weight one. Those changes made a huge improvement. Now I can use a minus connector and not have a horrible trigger pull.