Man!!! You're a genius! lol
As simple as it may seem, the problem was in the PCI Express X16 contact. I used an electronic contact cleaner and it was solved! As you said, if i look at the GPUZ, it was fixed at PCI Express X16 4.0 @ X1 3.0. After cleaning, it was at PCI Express X16 4.0 @ X16 3.0...