Newbie needs help getting HD thru Roamio

Hey,



I just got a new HDTV (Samsung 75") and a new Tivo (Roamio HD).



Xfinity came in and placed a cable card. Appears to work well. All the channels come in.



Any time I watch Netflix or Amazon through the Tivo, I see HD quality content. Unfortunately, channel surfing results in all SD quality programming.



I'm new to HD in general. The Xfinity cable guy hasn't been any help.



Is this lack of HD due to poor signal quality? A problem with the cable card? Do I need to upgrade my cable package?



Thanks, in advance, for your help.



Ajay