epmp1800? is this a variant for another area? :joking: Do you mean ePMP Force 180 or epmp1000?
40dBi antenna? that would be a fairly large dish antenna of about 2m (6ft)! if you set this, please set it correctly to the actual antenna gain or you will get false information.
First thanks for the link stats but they dont really help, they just say that link wise, everything is fine. If you are the admin for this radio (not a customer having issues) then we will need more of the config (of course we dont need IP or MAC info) including which firmware you are running.
low bandwidth issues (from the ethernet side of things) is usually related to smart speed being enabled or MTU or arp cache timeouts. Not all devices properly implement this feature and if you have a device that has low-power ethernet features then the epmp radios tend to do weird things with smart speed enabled. MTU needs to be at least 1500 unless you are using additional l2/l3 protocols then it should be at least 1536. If you are using pppoe then mss clamping needs to be enabled.