Get 5Ghz on laptop.

SOURCE: toshiba laptop to airport extreme cannot get connection

how old is the toshiba laptop? It might not be able to use WPA2.

SOURCE: Airport extreme / Windows XP with VPN problem

have you reset the airport extreme? theres a tiny hole you can push in w a paperclip. Also, do you have the latest firmware?

SOURCE: Internet connection drops within 5 min after (re)booting Airport

Speak with your internet provider, it sounds to me that the apple people didnt know what the problem was without getting down and dirtyy with it so they replaced it hoping for an easy fix. Seems to me that either the internet signal is being interrupted between the isp and your home .. or the motorola modem is having problems. I have never been a fan of motorola modems to begin with. Also the rentals u get from cable companies are used.. and typically subpar bottom of the line equipment that fail often. IF you think you will be using cable internet for years to come, purchase a linksys modem, as it is you are paying $3-5 a month for the rental of the modem. But I digress, speak with your isp and see if they cant troubleshoot the problem.. if 2 airports are having the same problem the chances of it being the airport... slim to none. good luck with all of this post again if nothing changes.

SOURCE: When router is connected to D-link modem, no

Try running this test... I got it from a Comcast technician who came out when I had same problem.
Look for any failures or anomolies. Look at the signal page and check to make sure the signal to noise ratio is in the 30's or low 40's. If higher, call Comcast and tell them.
http://192.168.100.1/index.htm

SOURCE: I have an apple router.

It's a common problem with wireless routers, especially with certain ISP's, there's several theories about why this happens including cheap parts and software on the routers but it can be much worse if it's over a cable connection. Possibly because the MTU is higher on cable networks than wireless ones. This issue doesn't seem to affect wired connections to the routers as much. ie you may still get a working wired connection even if the wireless isn't working.

Certain makes are known to behave this way, with certain ISP's. eg in england there's a cable company called virgin media, belkin routers really don't seem to like them, but netgear seem to work much better, which is probably why virgin recommend netgear and will only supply netgear routers themselves.

Try changing the channel id if it's wireless, as there may be a lot of interference around you and this may or may not have a bearing on this issue. If that doesn't help then ask your isp what make they recommend as they should have an idea of what will work best, at least the tech support dept should.

In my opinion the best makes of routers are netgear and linksys. I also like belkin although they aren't as good as they used to be, and as mentioned can suffer from this problem quite badly in some cases. As you are with a cable

You will never completely eradicate this problem, all wireless routers will need resetting now and again, but it should be weeks or preferably months between each time. Cisco routers may be more reliable but they're business routers and are very expensive, and probably a bit more complicated to setup.

ps. I used to work for virgin media as tech support.