Pixellation is (more often than not) a symptom of poor TV signal. If your V6 downstairs is fine, that proves the cabling as (most likely) ok as far as your outside termination point.
If you can swap the boxes around, see where the fault follows. That should help ID whether the TiVo is at fault, or there's a problem with the internal cabling.
Then you can report the problem to VM, knowing (pretty well) where the issue lies.
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