Asus RT-AC53U - Drastically Slower Speeds Than Direct Modem Connection

When I connect to my PC (hard wired) I get around 50 MBPS. However, if I connect directly to my modem I am getting the full ISP amount 120 MBPS.

I've made sure it's not the cables (all tested the same way) I've also checked on other forums and tried their recommend fixes such as disabling QoS (which didn't do much). I also tried to disable the NAT but, that ended up causing a whole bunch of other issues.