Hi MacinMan... I recently got the same router (ax86u) and am noticing that I rarely get full wi-fi speeds on my Apple devices (MBP, iPad, iPhone etc.). Just wondering if you notice anything similar?
My internet service is 300 down and 20 up. I verified that the router itself is getting the full speed.
Here is the router speed test:
And here are some speed test numbers from my iPad for example:
This is standing about 10 feet in front of the router. I'm just trying to determine if this is a wi-fi issue or an Apple device issue. Just curious if you are able to obtain consistent full speeds on your Apple devices?
I can't speak for AT&T (which it appears that you have.) I have Spectrum, so I only have a modem, I believe AT&T gives a combo unit which has to be adjusted to take a separate router.
What I can say is this make sure you have your WiFi settings correct.
Set the 2.4 band to 20Mhz, and channel 6 works good for me
Set the 5Ghz to 20/40/80Mhz, because Apple devices don't support 160Mhz channels, disable it, so your max is 80Mhz, if you have a non apple device that supports it, leave it enabled, but set the wireless channel to 36 for 5Ghz. I have the best results, and get up to 8xx Mbps down on my iPhone 12 Pro Max and between 5xx and 7xx, sometimes up to 9xx on my Late 2013 13" MBP, the iMac is wired. I have Spectrum 1Gb package.
Beyond that, look up the settings on the online Asus support. You may need to fine tune the router for your setup. I did, but not so much because of speed, but other compatibility issues with smart home devices such as bulbs.
Hope this helps, After making the changes and apply them, give the router a reboot, and also your devices, and try again.
Hopefully these suggestions will get you started.
Let me know if you still have issues, and I'll go into more detail for settings to tweak.