I would try to connect with the ISP modem if you can, put your LT in the DMZ on the MODEM. I would not connect with the 825.
A preferred method to using the 825 fully would be to Bridge the ISP modem, however some U-Verse modems can't be. I this case, you can try to put the 825 in the Modems DMZ. Then the 825 should get all connections with out any modem interferences processing. Disable or Turn OFF the WiFi on the Modem. This is again, a preferred method.
Good luck.