I cannot understand why the dopey moderators have not told you this already, but there is a known fault with TiVo.
Please see the following thread:
http://community.virginmedia.com/t5/Virgin-Media-TiVo-service/Slow-TiVo/td-p/3195456
Please see the following thread:
http://community.virginmedia.com/t5/Virgin-Media-TiVo-service/Slow-TiVo/td-p/3195456