Pixelation started for Cable when upgraded to Unlimited Data and xFiComplete

I realize this seems strange since the Internet access is not related to the Cable TV signals.  But my service was working great for Internet and TV Cable.  A change I made in July was to upgrade to Unlimited Internet.  Doing this the store convinced me to change from my own Internet Modem to the xFi Complete Gateway since it would be cheaper than using my own modem.  I did this putting the Xfinity X8 Modem into Bridge Mode and continued to use my own Router as setup before.  The Internet access is fine, and streaming is fine.  The problem is that my Cable signal is now causing Pixelation on the TV's.  No change was made to the TV's with this change.  Question is that when moving to Unlimited Internet did Xfinity do something to the quality of my signal which would all of a sudden cause a Pixelation on the Cable TV channels.  I suppose the next step would be to convert back to my own modem, but Xfinity is going to charge me more for doing that.  Why does Xfinity charge more if you want to use your own modem, why would they have this pricing policy?  

Thanks for any thoughts.