Github is currently (on 22nd of feb 2012, again on 5th of sept 2016) having some problems with pushing/pulling over ssh. you can try if https://status.github.com/ shows signs of things slowing down.
You can try pushing over https by following this guide: https://help.github.com/articles/using-ssh-over-the-https-port/ This would only help if https is not affected.
Graphs where the mean response time goes up means there are issues (or possibly a DDOS) at github, and not at your end.
If github is currently being DDOS'ed they may choose to enable DDOS protection from a 3rd party.
Luckily, the nice people at the AT&T forum have found a workaround.
Making it work requires configuring both the NVG510 and the router manually.
Then use the address from the NVG510 configuration page under "Broadband-Gateway IPv4 Address" as the gateway address and the DNS server addresses from question #4 above as the primary and secondary addresses.
I took that command from Git's Testing your SSH connection guide, which is part of the greater Connecting to Git Hub with with SSH guide.
Then, in this router, set the DNS servers manually.
To see how to do all of these, see question 6 below describing how to force the NVG510 into "bridge" mode.
Where precisely, you will learn from DENIC's regional domain statistics.
read more DENIC, eco - Association of the Internet Industry and the City of Hamburg to host the international congress attended by the tech community, politics, industry, and civil society, taking decisions on the core functions of the Internet.
Two things to note: (a) The DNS server addresses to use appear in the log above, and also in the NVG510 Broadband-Status menu as "Primary DNS" and "Secondary DNS". However, from my experience (in the SF Bay Area), using Google's DNS significantly improves the network performance.