[AB] Arris SBG6782 DNS override not working (newer firmware?)

I use unblock-us's dns servers usually but, using them on this modem breaks my internet connection all together. After some searching, Comcast users were having similar problems with this device that were remedied with a firmware update. Does anyone know how to get firmware for these? Mine is running SBG6X82-8.5.0.0-GA-04-13-NOSH while the working Comcast ones are SBG6X82-8.6.0.0-GA-01-971-NOSH and apparently that version has this DNS problem fixed.