You can go to http://testmy.net/, create an account, and run some download tests under that account. Connect a single device directly to the modem using an Ethernet cable (NO ROUTER)Run some tests using the manual 12MB test size for download tests, and the 2MB size for upload tests, though the download speed is more of a concern, here. Run a batch of at least three tests, each one spaced five minutes apart. If you can, it would be best to run a batch of tests at different times of the day, preferably morning, afternoon and evening.
After you have run some tests, click on the "Results" tab and copy and paste the URL from the Results page into a post. This will allow the tests to be looked at.
It's important to create the account and run the tests under the account created. This will keep all of the test results in a central location, allowing them to be looked at for patterns.
It's also VERY important to make sure that you are using only a single device, connected directly to the modem, when running the tests. The router can add problems, which is why it needs to be eliminated when doing the tests.