I'm probably wrong, but I believe the guide you are using is the DirecTV guide, and I thought the difference was that that guide has its information downloaded from the satellite every time you move within it. If that's the case, then it wouldn't necessarily be a hardware issue with the Tivo, just an issue that they don't give you the choice of using both styles with the Tivo information.

The problem is that I like both guides equally, but they do seem to function better depending on the situation. I tend to watch the same channels all the time, so with the Tivo guide open I can simply go to each channel and see what will be on for nearly the rest of the day in one glance. However, with the grid-style DirecTV guide, I can look at all the networks or all the HBOs at once and see what's on all of them in the next couple hours. I think I prefer the Tivo guide because I rarely find myself in the second situation, and if I do, I can just click through them.