These drops in signal is just the AC66U . I have 1 laptop Dell Inspiron 1720 and 2 stationary PC:s all with Asus USB-N53 and get this issue. Asus equipment should work against each other I hope . When I connect to my backup-router a TP-Link WDR4300 dualband I gave no such issues. The only thing about the TP-Link is that the signal strength is about .14 dBm lower on the 5 GHz band compared to the Asus.
I am wondering if this 5 GHz drop issue is unique to certain wifi adapters, certain network environments (interference ir very stong signals), certain router settings or a combination of several of these factors since only 3 people are noting it.
I recall having an issue with my Linksys E4200 v1 router when I had it (before getting my N66U and AC66U): The 2.4 GHz signal would degrade and the unit would stop working within a day each time I reset it.
It turned out to be due to my Rosewill wifi LAN utility of all things (like SSIDer in terms of giving me network stats).
I disabled the utility (kept using the adapter) and the problem disappeared.
Just an example but I wanted to illustrate how a problem can affect some and not others and in certain cases have nothing to do with the product experiencing issues.
It may be worth experimenting with different wifi clients, trying wifi adapters in different locations of your residences, turning off some devices in the network, trying different adapter drivers *, disabling network utilities or some programs that access the net etc.
It could be the router but experimenting with other network components in an effort to rule out an issue not due to the router can't hurt (other than the time invested).
If I have the time (one arm is in a cast at the moment) I may unwrap my AC66U this weekend to try.
Part of me is considering holding off though in case this is a router issue and does not get resolved so I can still sell my AC66U as new and stick with my N66U.
* E.g. I experienced much lower wifi throughput after upgrading to Windows 8. I then looked for Windows 8 drivers, found some for my USB adapter's chipset (no package released officially for my actual device), installed the drivers and noticed a huge improvement in performance after going to the Ralink site and getting the latest wifi adapter drivers which Rosewill was not offering [yet]). It worked with the Rosewill drivers (just much slower) so you would not know to upgrade unless you ran speed tests.