I'm not sure why people still don't understand that having a "beast" computer and a high-tier internet plan doesn't mean that issues can't be on their side.
First of all: speed-test doesn't mean a thing, download speeds, upload speeds and ping to a server nearby you over less than a minute connection have virtually nothing to do with your connection to a game server that's probably *not* nearby you. Secondly, it's packet loss and instability that cause your connection to reset and it typically has nothing to do with either your connection speed or the game servers.
The thing you need to realize is this: the game servers don't typically have issues. They sit at a data-center and wait for information to come to them, the data-center has more than enough bandwidth to service the servers and server-side issues that aren't patch-related are INCREDIBLY rare. What happens more often is that part of an ISPs backbone will go out and cause people in certain area's or with certain ISPs to go down (ones in the path of the typical route to the servers).
In other words - it's your ISP. It doesn't matter if it's literally on your end (at your home) or a part of their backbone, it could even be another ISP that is leasing infrastructure to your ISP. The important thing is that it's not on Blizzards side. If it was "server issues" (which is flung around far too much) then EVERYONE would have the same problem, it wouldn't matter where they are located. There would be a technical support post detailing the issue and every forum would be absolutely flooded with posts about it.
Except that it's not on Blizzard's end. I've had no lag or DCs at all since the first few months of the original games launch, and a very short period of time around RoS when all the DDOS attacks directed at gaming companies (LoL especially) were happening. I don't get rubberbanding, I don't get disconnects, I have stellar ping and everything is super responsive.
So I suggest you get some packet loss logs and contact your ISP, that's where your problem is.