I had a similar problem myself, solved it by altering the 'port settings'.
Assuming you are running windows, try this.
In 'dialup networking' right click on your chosen connection. Click on 'properties' then 'configure' then 'connection' then 'port settings'. You will see two buffer sliders, which basically control the speed of your connection. Slide both of these over to the right. Doing this sped up my connection from typically 33kbps to always over 50kbps. Good Luck.
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Horry Snr.