M17x R4 Internet download issues

Hi all .. I have been having issues with my M17x R4 in that whenever I download from the internet either wireless or hard wired the download speed starts OK but then slows to an absolute crawl, most of the time I have to restart the download. There does not seem to be a link to the size of the download although small files download before the speed slows so is fine. I have done a complete re-install of the system including all drivers but this problem has not gone away. does anyone have any thoughts / suggestions as to what might be the problem? I have another alienware laptop that is working perfectly with the internet and hence it is not a router / ISP problem. Many thanks for looking.