So for those of you struggling with the same problem I have, the answer is truly proven to be Comcast lying to you.
After purchasing 5 different cable modems, I settled on a pricey Motorola. The ethernet signal was great, but the wifi was terrible. I learned about wifi analyzers for phones and changed my wifi channel away from neighbors, which has since solved that dilema...
BUT NOW... we enjoy the random slowness effect (RSE). It's Comcast. You can test this in many ways, the easiest way is to check LAN vs. WAN and make sure they're both super slow. Power off (and/or unplug power) your gateway (router/modem) for at least 10 minutes. After it powers back on and you have internet, repeat the LAN and WAN speed tests to confirm their both still in the gutter.
From this point you now must test your local WAN. I have a security camera connected to wifi that steadily streams 24/7. The streaming quality shows KB/S and the speed is maxed out in HD quality, despite the fact that my internet speed tests at 0.15 mbps download. That proves my gateway is doing exactly what it should be and it's the Comcast service that's crawling.
What's really mind boggling is why? Heavy internet usage / traffic? I go from 100mbps on LAN down to 0.10 for NO REASON for a matter of hours randomly week by week... and then, again for NO REASON, it will magically jump back up to full 100mbps speed.
I'll also note my service was installed less than 12 months ago, new cable buried in the ground, and it has been solid 90% of the time. I'm just getting real sick of Comcast's lame excuses constantly blaming our equipment despite the problem being on their end and they are too afraid or ashamed to admit their flaws. If you're like me and you have these random bouts, don't freak out, don't buy a new box, don't call a service tech, just wait an hour or two and try again. THEN freak out.
Squeaky wheel gets the grease!
Report it every dang time until they run out of space for notes on your account. Get a credit for the slow speeds while you're at it if the rep can enter it correctly.
I'm just getting real sick of Comcast's lame excuses constantly blaming our equipment despite the problem being on their end and they are too afraid or ashamed to admit their flaws. If you're like me and you have these random bouts, don't freak out, don't buy a new box, don't call a service tech, just wait an hour or two and try again. THEN freak out.
It's not normal to have substandard service and there is no reason to accept it. Start here to troubleshoot. Post your signal levels and equipment details if you still need help.