I am trying to use my Tivo to convert videotapes to DVD and I am having problems...

I am recording the programs onto the Tivo just fine, but the problems are coming when I try to extract and convert them. I am having different problems each time. Examples of problems are:

1) On some recordings I get errors while making the key files that say "No audio header found." When I mux the file I get video only. When I watch the program on the Tivo, though, there is sound. Why is my audio getting dropped?

2) On some recordings I get an error saying "No video or audio timestamp." These mux fine and the sound is in sync, but if I demux then remux with TMPGEnc the sound ends up being off by about 5 seconds. (This step is necessary because I am using a SA recorder that only captures 32khz)

3) On some recordings I get muxed video that when played in Media Player says it is, say, 1:23:55, but the video is actually only 1:23:50. The header lists the time as longer than it is.

I do not have these problems with programs that I record through my cable box. It's only the VCR recordings that are giving me trouble. Does anyone have any tricks or tips for making VCR recordings?