Hey CA3LE, just letting you know that they finally resolved the isslue. Tech support was useless even with the new information, and it took multiple calls to get them to send a technician out. When I complained, someone changed a setting on the line that made it stop working at all, and tried to tell me it was still working. "We cannot change it back. Your line is good sir!" They even tried to say that if it's not the modem, the testing sites must be at fault, even though other people were getting good results in the logs. Your explanation gave me confidence that it wasn't a problem with my modem, and we were correct. After a couple hours of troubleshooting, working on the equipment outside, and the tech having people on the phone do things like "change the atm path", he finally realized it was a bad line card in the box where the fiber and phone line connect. After replacing that card everything is working again.
Here are the new test results:
https://testmy.net/compID/992214742650
Not as fast as I'd like, but probably as good as it will get with the current setup. As you can see there are still speed differences between servers, but nothing drastic. Thanks again for this website.