Symmetrical Internet Speeds?

The current upstream / return path bandwidth spectrum allocation on DOCSIS is physically limited. It's the current nature of the beast. This is why there isn't as much flexibility in offering faster upload speeds compared to the download. 

Here  are informative articles about the future of the upstream bandwidth capability for DOCSIS based systems;
 

http://www.cablelabs.com/innovations/docsis3-1/  

https://arstechnica.com/information-technology/2020/10/comcast-says-gigabit-downloads-and-uploads-are-now-possible-over-cable/  

https://volpefirm.com/the-road-to-docsis-4-0/  

They do offer a 3 gigabit (with symmetrical speeds) FTTH (Fiber To The Home) service in some areas. It's named "Gigabit Pro".

What is the fastest upload available over their normal coax? Residential of course. 

Also, thank you for explaining.  

Currently it's 35 Mbps upload (around 42 with their 20% speed overprovisioning) with the Gigabit speed tier.