Have you tried changing the HDMI cable?

The TiVo Roamio will output in 1080P60(which scales everything), 1080P24(which is pass through only), and resolutions below this(which everything can also be scaled to)

 

Similar issue. I found my Roamio Pro was set to 480i about a week after I set it up. Found this because I could see it wasn't looking HD and the TV reported it was receiving a 480i signal. Spent an hour looking though the menus to find a way to fix it. The menu item can be found at: TiVo Central -> Settings and Messages -> Settings -> Video -> Video Output Format. I tested all formats and now all check boxes (video formats) are checked. It was set to use only 480i when I found this setting.

So mine can be set to 1080p but I left it with all check boxes checked. It was set by the utility that tests out video settings for me. I did not try to check that box myself. My TV shows it is receiving 1080i. It never changes to 1080p.

What I don't understand is how this value ever got set. Was it the default from the Tivo factory? Did I do this? Did the Roamio have a bad day and change the setting to 480i to meet an issue it detected? The install instructions did not ask me to check or change this setting.

 

So mine can be set to 1080p but I left it with all check boxes checked. It was set by the utility that tests out video settings for me. I did not try to check that box myself. My TV shows it is receiving 1080i. It never changes to 1080p.

With all resolutions enabled you won't ever get 1080p output if you only watch broadcast/cable TV, as all TV is currently broadcast in 480i/480p/720p/1080i. So with your settings you'd currently only see 1080p output from your TiVo when watching Netflix or other online sources.

If you disable the lower resolutions then the TiVo will upsample everything to 1080p. (This is what I do, as it gets rid of the long pause my Samsung LCD has when switching resolutions. And I find that the TiVo does a pretty good job of upsampling. Better than my Samsung at any rate.)

What I don't understand is how this value ever got set. Was it the default from the Tivo factory? Did I do this? Did the Roamio have a bad day and change the setting to 480i to meet an issue it detected? The install instructions did not ask me to check or change this setting.

Weird. I'm pretty sure mine prompted me to choose video output when I set it up. But maybe it didn't and instead I dug through the settings myself (as I would have, as I was quite excited to be upgrading to a TiVo model which supported 1080p)

 

Found the solution...

Actually had to change input from HDMI 1 to HDMI 2.

For some reason, the Tivo did not like HDMI 1.

 

...

What I don't understand is how this value ever got set. Was it the default from the Tivo factory? Did I do this? Did the Roamio have a bad day and change the setting to 480i to meet an issue it detected? The install instructions did not ask me to check or change this setting.

It looks at your TV's EDID,

http://en.wikipedia.org/wiki/Extended_display_identification_data

If it had issues with it I think it fails all the way back to 480i(i thought it was 480p though)