Paolo,
I agree with Larry that 87 hours is too long to ferment the dough, even if most of that time the temperature is only 55 degrees F. I think that your dough overfermented. When I normalized my numbers to fit your fermentation scenario, the results indicated that you were using about 1.38 times the amount of yeast that I used, on a normalized basis. The higher amount of yeast will accelerate the fermentation process. What usually happens when a dough is fermented too long is that the protease enzymes in the flour attack the gluten and weaken and degrade it. In the process, water is released from its chemical bond and results in a wet and clammy dough that does not make for a good end product. If you were using a round dough storage bowl container like a Rubbermaid or Glad type container, I think you would have observed a rise in the dough because the sides of the container would have contained the dough ball more than in an open DoughMate pizza tray. That was the reason why I asked you what you were using to store the dough balls during fermentation.
I do not believe that the 3% salt was responsible for your results. We have a few members who use around 3% salt, without incident.
Peter