are you using the standard WAN port or the 2.5G port to connect to your modem? I was using an Aris SB8200 but when I started having the issues I upgraded to the Aris S33. After downgrading the firmware both modems perform the same in the 700-800mbps range.
I had lots of issues with this firmware. Once I upgraded to it my internet speed dropped in half. I have 1GB from comcast and would consistently get 700-800mbps, after the upgrade I couldn't get over 390mbps. Connecting directly to my modem I'd get over 900mbps. I downgraded to 30043849566...