Low upload speed

The past couple of days I have had an issue with my upload speed being low. I have ran multiple tests on xfinity speed test and I am usually getting 2-3 mbps upload. I have the blast package and am getting 200-210 download. Earlier today, my upload spiked to 12 and stayed there for 10 minutes and I notice it dropped back down to 3. I spoke with customer service and they did multiple resets and told me everything is fine. I just recently started having this issue and trying to figure out what is causing it. My computer is hardwired. Any help would be appreciated.

Thanks