Apart from the ABC the rest have good Signal levels. You have not said, but I'm assuming that you have problems with more than just one group of channels?

As I mentioned originally with digital it is very important have good Signal Quality. A common problem in unit blocks is that they often use Signal Amplifiers fed by poor quality signals. So if you have a signal with a low signal to noise ratio to start with the noise component also gets boosted also by the amplifiers with can overload sensitive receivers.

Is there anything still using your units antenna outlets besides the TiVo (like the TV)? Might be worth unplugging everything just to see if it improves your issues.

Would still be good to try the box at a friends house, just to confirm you do not actually have faulty TiVo.

Peter.