some mirrors are just slow. the workaroudn is to first let tdm_update update itself thus downloading the initial files just before it makes you start the 2GB download after that exit, open (better with notepad++ so you get a proper newline) tdm_mirrors.txt and comment out the slow mirrors. In my case it was: #[Mirror fidcal.com]
#url = [url="http://www.fidcal.com/darkuser/"]http://www.fidcal.com/darkuser/[/url]
#weight = 6 after that start the tdm updater again but this time select the "Dont search for new mirrors from thedarkmod.com (--keep-mirrors)" option so the tdm_mirrors.txt wont get overwritten I've got decent 500-900 kbps from the other mirrors that way.