I'm having exactly the same issues over the past 7-10 days. My connection fails on an hourly basis or so and help via chat or on the phone has not provided any help. I keep being told the issues are with my equipment, but things have been fine for 3+ years and the log seem to indicate other issues:
Sun Jun 01 11:08:25 2014 Critical (3)
No Maintenance Broadcasts for Ranging opportunities received - T2 time-out;CM-MAC=<snip>;CMTS-MAC=<snip>;CM-QOS=1.0;CM-VER=3.0;
Sun Jun 01 11:08:15 2014 Critical (3)
No Ranging Response received - T3 time-out
Sun Jun 01 11:07:58 2014 Notice (6)
T4 No Station Maint Timeout - Reinitialize MAC...
Sun Jun 01 11:07:58 2014 Critical (3)
Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<snip>;CMTS-MAC=<snip>;CM-QOS=1.1;CM-VER=3.0;
Sun Jun 01 11:07:26 2014 Critical (3)
Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=<snip>;CMTS-MAC=<snip>;CM-QOS=1.1;CM-VER=3.0;
Sun Jun 01 11:00:41 2014 Notice (6)
TLV-11 - unrecognized OID;CM-MAC=<snip>;CMTS-MAC=<snip>;CM-QOS=1.1;CM-VER=3.0;
The T2/T3/T4 time-outs would seem to be an issue. I fear that I also suffer from older firmware, but since I own the modem, Comcast does not update it for me (currently running 6.5.2). Other ideas out there?