I don't think it's STM with 55 kb/s upload speed.
goto
http://192.168.100.1/ and look at your modem config pages, you should see one marked `Signal' go there and post the info on that page (power levels down and up stream and Signal to noise ratio for downstream). Someone will probably tell you if there's a problem with the figures.
Other than that get in touch with tech support, which you can do two ways. By telephone or newsgroup support and if you don't want to spend hours on the phone I suggest you try VM's newsgroup support.
For how to setup outlook express for newsgroups:
http://www.virginmedia.com/customers...setting-up.php
and the group you need to subscribe to is:
virginmedia.support.broadband.cable
Post on the above newsgroup with a description of your problems and see what they're got to say on the matter.