chh12, what happens if you reboot the CGN3? Will it temporarily restore the 200 Mb/s speeds?
You indicated that you also had cable. Is that for a single tv, or do you have more than one cable box up and running? Do you know where the splitter is located that splits the inbound feed cable into their respective paths, internet and tv?
Can you do a quick check for me, and that is to see if you have structured wiring installed. Easiest way to see this is to unscrew the screws holding a cable or phone wallplate to the electrical box behind it, and remove the wallplate just enough to see if there is a bundle of cables behind the wallplate. In total, connected and unconneted you should see two RG6 cables for satellite and cable tv, one Cat 5e ethernet cable for data and one Cat 3 (possibly another Cat 5e) for telephone. With a 10 year old house, I suspect you have the cable bundle installed. After having a quick look, reinstall the wallplate. Done. And, let me know what you find.