Is that slow download speed consistent on any download site? Browsing various sites is always slow? Download connections can vary, one might be extra slow, but if you cancel it and start another it will be faster. I'm not saying you are wrong about an issue, just checking.
Did you intstall the XFastLAN software? Not that you must have it, or that it would automatically help, just asking. That software has priority settings that might cause trouble.
If you click on the Network icon in Windows in the lower right corner, looks like a PC monitor, and then click on Local Area Connection, you can check your connection speed. You can also check the Broadcom network chip in Device Manager, its Properties and/or Advanced Properties for configuration settings.