Superfast Upload Speed Is not as Described

... 800/100 ... only getting around 20-24 for the upload speed ...

The best resource for this AFAIK is https://www.reddit.com/r/Comcast_Xfinity/wiki/knowledgebase/next-generation-internet/. It probably won't answer all your questions, but it's the best information I know of.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

Your Arris G36 isn't supported for increased upload.  Check the My Device info page: https://www.xfinity.com/support/devices/ and click on the "All Compatible Devices" link on the right side.  

Only 3 devices are currently approved for "next gen" speed.  You need one of those to get the increased upload, if it's even enabled in your area.  Comcast is slowly rolling it out to more locations and modems.  Currently only the Hitron CODA56, Hitron CODA and Netgear CM2050V are supported.  At first it was just the two Hitrons, then they added the Netgear CM2050V.  I have to assume they'll add more devices to the supported list and I'd guess your Arris G36 is probably on the list since it's one of the 4 devices the My Device Info web page recommends without opening up the "All Compatible Devices" .pdf.

You might be able to get increased upload by buying one of the 3 supported modems for increased upload and presumably a WiFi router since all three of them are straight modems.  I have a CM2050V but they haven't turned it on yet.  They've been crashing my modem in the middle of the night on weekends lately though and now I have an upstream OFDMA channel locked, so Comcast is doing something.  The web site says I have 1200/200, but get ~1420/40.  I'm not chomping at the bit for more upload, so I'll give them a couple more weeks before I show up at the store and bug them.  It's also worth noting that I am not in an area listed as a "current area" in that Reddit post BruceW linked.  I'm in the Chicago area, so that along with the recent crashes and sudden appearance of an OFDMA channel makes me think they're still working on it around here.

You could also rent a gateway if you want more upload fast.  That might not be a bad idea.  It would be much cheaper to rent for a few months than it is to buy a new modem and a WiFi router.  If you really need it a gateway is probably also the surest bet.  The rental gear gets support first.  I'd probably do that if I really needed more upload and didn't already own a supported modem... and immediately put it in bridge mode.  Of course it's also a bit of a gamble since it's possible they'll never add support for the Arris G36.  Unless you want a mesh kit... then buy a modem and a mesh kit and put that G36 on Craigslist or eBay.

@user_eauggq Good morning! I hope your weekend is going well so far. Thank you for reaching out to our Community Forums Team. I'm happy to take a closer look into your account and services, and provide the next best step to getting the increase in upload speed. To begin, can you please Direct Message your name and service address? 

Click "Sign In" if necessary
Click the "Direct Messaging" icon at the top of the page (looks like a text bubble)
Click the "New message" (pencil and paper) icon
Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line
Type your message in the text area near the bottom of the window
Press Enter to send it

Good morning, Caifu! It's a pleasure to meet you. Thank you for sending over the account information I asked for, it's most helpful! I'm happy to look into your speeds today. In order to finish verifying your account, I will need to send you a verification code to your primary phone number or email address on file. Which method will work the best for you today?