Mellanox connectx4 MCX4121A-ACAT half bandwidth on pci4.0 4x?

Hello, I have the above card installed in a 4x slot and I noticed my respective bandwidth getting chopped in half, 10gbe link, 4.5-5 gbs max throughput. Is there a way or a setting for it to fully saturate the link? pcie3.0(since card only supports 3.0) 4x should get me 32 gbes, more than enough to saturate a 10gbe link