Unfortunately, I've never been good at interpretation; nothing like d_l
over in the AT&T forums. But, given the connection speed difference, and the normalcy of your speed in off-peak times, and the history of CenturyLink problems across their footprint, I am inclined to suspect router exhaustion. Generally only fixed by adding bandwidth; unless there is a less congested router available.
Not sure how the OOL test is run; but Java and Flash test results tend to be inconsistent. Maybe try "ShaperProbe"; it works with my ADSL2+ connection:
DiffProbe release. January 2012. Build 1008.
Shaper Detection Module.
Connected to server 188.8.131.52.
Upstream: 698 Kbps.
Downstream: 15950 Kbps.
The measurement will take upto 3.0 minutes. Please wait.
Checking for traffic shapers:
Upstream: No shaper detected.
Median received rate: 709 Kbps.
Downstream: No shaper detected.
Median received rate: 15642 Kbps.
~Oh Lord, why have you come
~To Konnyu, with the Lion and the Drum