Do you have a native output or hybrid mode set in Settings -> Video?
If you have a hybrid or native output mode set, the Tivo sends different channels in their original resolution, and displays must resync every time the resolution of the input signal changes. Some displays can resync in less than a second, while others can take four seconds or more.
If you set TivoHD to Fixed 720p or Fixed 1080i, it will convert all channels to that format so there is no display resyncing necessary.
If you have a hybrid or native output mode set, the Tivo sends different channels in their original resolution, and displays must resync every time the resolution of the input signal changes. Some displays can resync in less than a second, while others can take four seconds or more.
If you set TivoHD to Fixed 720p or Fixed 1080i, it will convert all channels to that format so there is no display resyncing necessary.