Personally, i think you're better leaving Tivo in the proper 'panel' mode and if you want to change the picture for specific shows, use your TVs aspect ratio settings.
I pretty much always watch 4:3 in their correct aspect ratio and get the black bars down the side. But sometimes, I will zoom the picture, though that sometimes leads to a poor quality picture, so i go back to 4:3.
On TCM, they tend to show movies in the 16:9 aspect ratio, but within a 4:3 frame. Zoom works fairly well for these and you don't lose any of the picture.
I never use the strech mode as although it's meant to keep the centre of the picture in proportion and strech the outer part of the picture, it still loks awfull to me.
On any VM installation i've had, the installer always leaves it in the wrong aspect ratio, i.e., wide and i have to go in and change it. For the way you seem to prefer it, it sounds like you were unlucky and got one of the few installers who knew what he was doing
