@Cali88 Hi, I also did exactly the same.. purchased the AX6000 to replace my C5400 and was experiencing the exact same issue. What I did (and as far as I can tell since I just made this change yesterday night) was to disable the AX standard for both bands and left 2.4Ghz with b/g/n mixed and the 5Ghz with a/n/ac mixed modes.

I guess this is an issue related to the AX performance which would make a lot of sense that with a future improvement on the firmware of the router, would get fixed. Hopefully it is soon. I would try this change on your router´s settings and put it to the test. Hope it helps! :-)

@djviko I gave it a shot and after changing the settings it's barely reaching 200Mbps. 180-195. I tried plugging the older router back in and it got 515 on the first try. 🤷‍♂️

@Cali88 Did you put back the 5Ghz channel to Auto selection? Are you sure your device where you are testing speed is connected to the 5Ghz band or are you doing the speed test directly on the router? If the device is connected to the 2.4Ghz band, speeds would for sure be much slower, just wanted to point this out so you make sure the test is being done on the 5Ghz band...

Also, try to do a speed test directly on the Basic configuration of the router, would be a good idea to confirm your router is receiving the same speed from the modem... would be also good to check you are connecting the same ethernet cable on the same LAN port to confirm is not an issue with the LAN port/ethernet cable that connects to the router...

@djviko  I set everything back to auto, made sure I'm on 5ghz and still no luck. Getting between 180-230mbps with ax turned on again. It was slower with it off.  What's interesting is I did the speed test in the router settings and got a download speed of 530. So there's that. 

@Cali88 Hopefully someone from TP-Link support can answer to your inquiry so it can get fixed... sorry I was not on the correct path to fixing your issue... good luck with that!

@djviko I am having the exact same issue. Speeds are 1/3 to half the speeds on WIRED and wireless connections. If I swap my 4 year old router back (asus onhub) speeds are back in the gig range. This model IMHO is junk and needs massive firmware updates etc. I just purchased a tried and true tplink C4000 at Costco for 130$ and will be returning my ax6000! This junk should work out of the box with it's default settings taking into account the price we paid!

@Slendobeja I fixed the issue I was having....I went and got an Asus ax-11000. Smooth sailing now. Tp-Link should have tested, retested and tested again before releasing this router.

@Cali88 Thanks for the reply. There is just something off with the model... basically we all fell for their beta product and lost OUR time in the process. Good choice with asus!  I just plugged back in the free router spectrum gives user Instantly my speeds are 1/3 to 50 percent faster. I think I should look elsewhere besides the archer ax6000

@Cali88 , I also have slow speeds on my AX6000 that was purchased the last week of December. Unfortunately I did not put it into use untill yesterday when our Fiber from TDS was installed for our home business. Our Download speed direct wire (off the rear ports and to direct to modem) is >300 Mbs and >300 Mbs upload when it is packaged at 300/300 business line. Although the download speed by WiFi on 5ghz & 2.4ghz at apx 6 feet from the router is at best 165 Mbs down and 285 Mbs upload. Pretty consistent on speeds and download being basically 1/2 the rated speed. 

Really disappointed since my Google WiFi mesh is pretty good at being close to rated speed both up and down. Oh and only 1/2 the price. 

@Cali88 

I JUST got this router after a few youtube reviews raved about it. I have 500 down 50 up internet and now..wired I am lucky to get 5-6 Mps down - wireless it seems to cap at 50 Mbs no matter what. I just updated to the latest firmware - no change. My laptop is brand new with an ax wifi chip - same results. I cannot find a setting on here that would cause this. It is both wired and wireless. 

great - now I have to go return it and the store I had to get it from was an hour away - everyone close to me is out of wifi routers thanks to covid and work form home. Last TP link product I buy.