Q: Connectivity Issues with A1143 Airport Extreme

Looking for some help in diagnosing an issue I'm having. I've had this Airport Extreme for several years now, maybe close to 10. Lately I am having a ton of issues with connectivity being either very poor, or dropping constantly. All Airport firmware is up to date. All software updates for all devices are up to date.

Devices on network...

ATV 3rd gen

ATV 4th gen

iPhone 6

iPhone 6s

iPhone 5c

iPad 3rd gen

iMac

MacBook

3 Airport Express stations used for streaming music

Issues I'm facing...

1. Airport Extreme will drop wifi, so have to unplug and plug in

2. iPhone 6 used the most, and will show very poor or no wifi signal even standing in garage 15 ft away from Airport Extreme with one studded wall between us.

3. Airport Express stations will not show up sometimes to stream music

4. When I can steam music, sometimes it will keep cutting out.

I keep thinking maybe something is wrong with my iPhone 6, but then I try streaming music from my Macbook, and it keeps cutting out. Yet my friend hops on his Macbook (a much older one) and streams with no issues. So it happens on multiple devices in my home.

I know this is not a dual band router, and I have been told mixed stories about whether or not I can set device priorities on this router. Or even if that would help. And if someone said for certain that my router just can't handle all my stuff, and upgrading to the new dual band one would solve my issues, I'd do it. But it never used to be an issue, and nothing really has changed that I am aware of.

Any help would be greatly appreciated. I'm a very tech savvy guy, but wifi and networks has never been my strong suit.

Thanks!