networking in Linux ONLY, really slow

I currently have a desktop running Slackware64-current that's been experiencing painfully slow WAN speeds. I've tried booting off of different versions of Slackware live, systemrescuecd, as well as Parted Magic and they all seem to experience the same slow speeds when accessing any Internet related traffic. The interesting bit is when I dual boot from the same machine into the Windows partition that I get almost the max Internet speed from my provider. This same desktop is connected to a dumb switch that's not capable of VLAN, however my router/switch is set up for VLANs, a mikrotik. The port this dumb switch is connected to on the mikrotik is set to be untagged so it should not have any effect. Other than that I'm at a loss as to why only the Linux side of things is getting affected. iperf3 to machines on the LAN gets me the full 1Gb speed so it seems like only the WAN is affected. Any ideas?