I advise you to configure the router through the internet browser.

Changing to 8.8.8.8 and 8.8.4.4 did not change anything. What kind of problem do you have? Please describe it carefully.

I think that is problem with USB power performance. You have to connect modem by the active USB hub.

Does the latest TP-LINK 'official' firmware include the Beta patch to get the issue fixed? Sorry I can't give you info about that because I haven't tested this last official firmware. I use last beta...

My "beta" collection - ftp://tplink-forum.pl/Beta/ and last firmware - Archer C7_V1_140704 from TP-link website.

http://tplink-forum.pl/faq-basic-networking-concepts/how-to-configure-tp-link-td-w8968-wireless-n-adsl-modem/