I believe this is a issue between your ISP and amazon. Not really sure how to test that, but you could try the speed test at this site. First deselect "Content Delivery Networks (CDN)". Then click the select link behind "Cloud Servers" Click "none" in the upper right corner of the window that popped up. Select only "AWS EC2", press save, and start the test. If the speed test don't show any problems, try selecting only the service region you'r in (just above the start button) and run the test again.