Hi Kim

I'm not a networking expert but given nobody else has replied I shall pass on some comments:

TiVo should not interfere with your network and definitely not something as predictable as something noticeable at the end of a recording. The daily call for guide data is only brief and not much gets transferred. At ADSL2+ speeds it would not be for any significant amount of time.

One thing you can do right now to rule out the TiVo is disconnect it from the network. The TiVo will still function with retained guide data for a few days before it complains of no guide data - but even then it can still be used for manual recording and playback. See if that makes a difference to your transfer speed problems.

Also is the TiVo wired ethernet or have you made it wireless with a Wireless Bridge or similar?