I have the lastest firewire and airport utility
It is firmware.. but I get what you mean.
Sorry this issue comes up for some people. I don't think there is a lot that we can do to fix it.
When the wireless has dropped out try opening a terminal on the computer and ping the TC..
The command is simply ping 10.0.1.1
Assuming you haven't changed the IP of the TC. Use Control + C to stop the command.
If the TC itself refuses to respond then I would take it back to apple for replacement. If ping still responds the TC link by wireless is still working .. it has dropped internet. Which is another issue.
There are a number of people with the new AC model TC and AE posting with wireless dropout issues. But yours are particularly severe.
Some things you can try.. make sure the names in the TC are all short, no spaces and pure alphanumeric.
eg TC would be fine for TC name.
TC24ghz is fine for 2.4ghz band
Give 5ghz a different name.. just while you try and sort the problem.
TC5ghz is fine for 5ghz band
The disk share name should be data by default.. that is fine.
Now also set the wireless channels.. there are only 3 non overlapping at 2.4ghz.. 1, 6, 11 try each of those.
For 5ghz try forcing it to 40 or 48 or even lower if available. 36 .. then try the high channels. 157 or something near.
No luck just return it.
Apple have removed almost all diagnostics from the TC so there is almost no way to trouble shoot.. it works or not.