Sometimes if you are downloading a file and you are at 43% and someone else decides to download that same file it can cut your download speed. Go into Tools>Options. Click on the + next to Uploads then click on Basic. In the third box that's titled 'Partial Files' you will see 'Allow Partial Sharing' and the box is most likely checked. Click off the check mark. Give it a try. It might be the cause of your problem!