From what I found out on my Mother Board is 1 of 2 things going on here. 1. The BIOS is set to x1 for that slot even though it's an x4. 2. That slot is sharing another slot and maybe slowing both slots down.
Note: I can slow my x16 to x1, x2, x4, and x8. Plus, I can also change the PCIe 3.0 to...