I have successfully used Wonder Shaper for some time to help my “temperamental” Comcast cable modem connection.   I am able to upload/download while surfing and using a VoIP line.
I recently did a clean install of the custom 6.01.  My 3000+/256 Comcast line tests averaged around 2100/150 over a 10 day period.  I added the QOS panel and tried several settings over 2 weeks and achieved a small improvement.   I re installed Wonder Shaper and again saw a dramatic improvement.  My connection is averaging 3050+/225-248.   
Take a look.  Below is a link to the rpm I used.
http://lartc.org/wondershaper/