@Cali88 

This week, i made some big changes to my internet.

Went from 400 Mbps to 1.2 Gbps. This required a modem update to a DOCS 3.1 to support the high speeds.

Since this Archer AX6000 has a 2.5 Gbps WAN (Internet) port, I got the Netgear Nighthawk CM2000 modem, which has a 2.5 Gbps outbound port to use with the AX6000.

I learned and caught bunch of stuff, some already mentioned in this forum. My issues ARE now resolved, and i'll explain them below.

1. You need to make sure you are using a COAX splitter that is good quality. I had a splitter and it caused randomized speed test results anywhere from 500 - 900 Mbps when directly wired into modem. Once I removed the splitter and went right into the modem, I was able to get 950+ Mbps consistently.

2. Removing Smart Connect feature on the WiFi options of the AX6000 boosted my speeds. (noted in the image at the end of this post)

        This is also needed in order to enable the MIMO function under 5Ghz setting, which also boosted my speeds a little. (noted in the image at the end of this post)

3. Setting the QOS speeds manually did help speeds slightly.  I maxxed this out to both @ 2499, essentially removing QOS.

4. Removing the Antivius functions also increased some of the speed. 

5. Finally, setting the proper channel in your 5 GHz band IS CRITICAL. With 160 MHz you should set the channel manually to 36. Leaving this as "auto" might work, but it might not, better to set statically to 36.

My WiFi connection status states 1.2 Gbps speed, so my download speeds are roughly 600 Mbps on Wifi. Wifi (including WiFi 6) are all half duplex, vs a wired connections full duplex. What this means is that you'll see speed results at half your connected status. If this sounds confusing, that is because it is a little confusing. Which lead me to the final fix (step 6).

6. In the 5 GHz settings of the Advanced Router settings, I changed my band width from "auto" to "160 MHz ". (noted in the image at the end of this post) I didn't realize it, but my WiFi 6 devices were all grabbing the 80hz when it was on auto. Once I set it to 160 MHz, my speed status doubled to 2.4 Gbps on WiFi 6 client device status (when very close to the router). As I'll explain below, WiFi is half duplex, so you'll need 2.4 Gbps to actually get a 1.2 Gbps connection. All lower frequencies still work with this setting statically set to 160 by the way, so you don't need to worry about this breaking non WiFi 6 clients that only support 20/40/80 frequincies. 

To explain Duplex speeds further....

In short, if you're wired at 1 Gpbs speed (which is FULL DUPLEX), you'll get the full speed or very close to it. In my case its about 950 Mbps internet speed.

if you're WiFi at 1.2 Gbps speed (which is HALF DUPLEX), then you'll see around 600 Mbps internet speed. Since WiFi is also a bit unreliable, its normal to see this fall between 550-620 Mbps. If you get your WiFi to be 2.4 Gbps (or better), now you are theoretically faster than standard gig Ethernet wired connection!

Its a common misconception that WiFi is full duplex, and I think that causes some confusion. There are also many other factors in here as well, such as tri-band (this router is dual band). As a good rule of thumb, just remember that your actual internet/network speed will be half your connected WiFi speed, or a max of whatever your ISP gives you.

Here is an image of my settings, maybe it'll help someone: *DO NOT SET CHANNEL to 100 as I've shown below, set it to 36*

After the above adjustments were made, my WiFi status went from 1.2 Gbps to 2.4 Gbps as I'd noted. As a result my internet speed test went from a max of 600 (ish) Mbps download speed to match my Ethernet speeds of about 950+ Mbps. Screenshot below:

@FelipeDuarte That fixed my speed issue.

@VRTS Super. This is a Good News.

AX6000 is a good Router, but the guys dont have investing the time to understand the problems, is more simple just purchase another.

But, we need know this router are running the linux embbeded server.  This is super or not, because many services running on the server, more cache, more traffic, more rules to rout, more firewall, more another easy services degrades the performance. I have many machines plugged in ethernet and wifi (2.4+5G).

How the @Jeads  said, tuning the parameters depends on quality of your hardware. For me I have a good cable the Wan connected on AX Router (Bridge Mode). But other optimizations we needed, how to disable IPTV,  I tested the best MTU from router to fiber modem (MTU 1452 - The bests), but the difference I encountred was in simple a configuration, the dns herded from ISP is a bad DNS, and the routing of anything internet address was so slowly, but so slowly to open a google.com.br. After setting the fixed dns and I say the google dns (8.8.8.8, 8.8.4.4), I had an automatic speedy upgrade, 100mb to 300~350. (My contract is 300Mb), >300Mb is a good speedy for me.
I have 3 kids, (n) devices plugged on wifi, rockpi cluster, xbox etc.
How @Jeads , I disable the smart connect, OFDMA is enable.
Then if I make list of important configuration for me, i writing 5 steps to my success:

1 - Set the QoS manually to Max Size
2 - Define the device of get the preference  of traffic in QoS. In my Case, my phone and my laptop have receive the grant of preference, but just two devices.
3 - Set a fixed DNS, I don't know why the router don't resolve the route correctly, sometimes isp sending the same dns but doen't work correctly.
4 - Schedule the reboot router every day (this is importante, because the traffic is so much high and the performance of download reduce to a half of total, and some cases i seeyd the router with the freeze state)
5 - disable features not used, this is a good pratice, how balloo the bear sing in Mogli carton: Bare Necessities. E.g.(IPTV, FTP. H323,etc)

And upgrade your firmware to last, because I had an incident with one hacker, he conected in my VPN (PPTP), but this feature was disabled in that moment. I found him because the internet on that point so was slowly, and don't had much devices working at time.
I get the logs, etc. My friend said for me: You are crazy, this is impossible. But is don't.
This is the fix of vpn issue.
------------------------------------------------------------
Archer AX6000(US)_V1_210223
ChangeLog:
* New Features/Enhancement
* Enhanced the security of PPTP VPN
------------------------------------------------------------
Then good night, so sorry for my bad english. I trying, but old guy dont lerning anymore.

Just It,
I hope this help more people, the router is not bad and is a good option compared with anothers one of category, just give the time to get the best configuration for you.

Thanks for you mensagem @VRTS , good night or day. heeheh