I'm pretty sure your downloading at 74% of the max speed you can get, if I have guess properly.
Now this is a thing that confuses lots of people especially non IT savvy people. Connect Rate is measured in Kb/s (or Kbs same thing, the s just mean per second), Mb/s, Gb/s etc etc, which is short for Kilobits, Megabits and Gigabits per second etc etc, key thing being connect rate is measured in bits per second. And Connect rate is the rate that you are physically connected to something at.
Now Transfer Rate is measured in KB/s, MB/s, GB/s etc which is short for Kiobytes, Megabytes, and Gigabytes per second etc etc, key thing in transfer rate is it is measured in Bytes per second due to the fact that storage is also measured in Bytes. Transfer rate is the rate that data is being moved at, and transfer rate cannot exceed the connect rate.
b (little b) for bit, and big B for byte, remember that.
Now there are 8 bits in 1 byte. (so 680 kilobits is 85 kilobytes)
And I'm pretty sure you saw the downloading file transfer rate in KBps (kilobytes per sec) instead of kbps (kilobits per sec), as in the electronic industry its been made a standard to measure transfer rates in bytes per second, so you should never see any transfer rate measured in kbps (kilobits per second).
So with a connect rate of 680Kbps your MAX transfer rate is 680/8 = 85KB/s.
The reason why you may not be getting 85KB/s could be lots of reasons, your current connect rate may not be 680Mbps, as internet connection rates changes if a signal is dropped and re connected due to lots of variables over a long distance (weather, humidity, line quality, temperature, static, interference, line noise etc), the rate your are connected at is the Max stable rate you could be connected to at the time of reconnecting. You maybe connected at a different rate from when you asked AT&T. Severs on the other end may not upload that fast, or restrict the upload speeds, some bandwidth maybe used else where on the computer (say like Norton), or your computer doesn't have enough resources to process the data at a higher rate (though highly unlikely as 85Kbps is really slow for a computer, but average speed for internet).
anyways with a connect rate of about 680Kbps a download rate of 63KB/s is not bad and is about expected due to the variables.
Hope this clears up everything, and if you really did see kbps in downloading really slow lol and someone screwed up the programing.