Have you rebooted your terminal to see if it will pass BIST since then?
I think the modem only performs BIST during power on, so it might be worth a shot since Amanda isn't seeing any errors in the diagnostics.
Well, that did the trick. It now says passed instead of failed.
Speeds are still jumping around a lot - here's the latest: http://testmy.net/quickstats/slym
I'll run the tests for a few days and see how that goes. Like I said earlier, it's been going pretty good until yesterday. But maybe that's the normal busy time in the evenings I'm seeing. Well, except for the couple of tests last night that were 1.07 and 1.47mbps - hoping that was just an oddity.