This won't be everyone's issue with slow upload, but it's something to consider when considering options...
It was the AMP.
We live in the country and have only had cable to the house for five years. Before that, we had Primestar-Directv-HughesNet. Apparently, when the Comcast installer hooked us up, the old AMP was left, and the tech yesterday said it did not meet their specifications. The minute the tech changed it out yesterday, our upload speed went from under 1mbps to 6mbps.
This process has cost me a lot of money and a stupid amount of time, but it's fixed, yay.