I recently renewed my contract with Comcast and immediately after experienced speed drop. After a reboot of my modem, the speed was fine but 10 minutes later it dropped significantly. The first agent wanted to send a technician into my place - I knew that would be useless as I was sure the problem was not my router that was working perfectly fine the day before my renewal. I chatted with a second agent a little later after reading about the issue and he offered a much more reasonable solution. He checked my account and this is what he said:
" I see that Checks have found few error and Bugs which is causing such issue at your end, This Errors normally triggered when the location of the modem is changed Or have performed Too many resets.
I'll have to make manual changes and once done with that will release Commands towards device, I believe this will get the issue fixed as in 95% of the cases it Does get resolved."
And he was right. Ask the representative to perform what he did to resolve this issue before starting to switch modems or having a technician come to your home.
Reporting a day after and speed remained fast. If you are experiencing this drop of speed about 10 min. after rebooting (maybe also associated with renewing a plan) then talk to an agent to do the same (debug+release new commands) like the agent I chatted with did. Good Luck!