Slow downloads - all devices, all types of download, and Apple-only

Since it's a Mac Mini, I can't easily transport it to try another network, and I only have one at home. At home, I get really lousy T-Mobile signal, but I'll try Radio when I'm elsewhere.

However, this has never been a problem until the past week or two, and there are lots of similar reports in Discussions - Radio dropouts, slow app installs, etc. I suppose it's possible that tons of people have bad ISPs, but it seems a little hard to accept that that's the only issue.

Correct. My reference to T-Mobile was for my iPhone and iPad, so I can't try using T-Mobile instead of Wi-Fi on iOS until I take the phone/pad somewhere else with a decent signal (or another Wi-Fi).

No, I have one home CenturyLink DSL connection, which feeds my AirPort Extreme base station. My Mac Mini is connected to the base station by an Ethernet cable, while my iOS devices obviously use Wi-Fi. I don't get a good enough T-Mobile signal to try that at home, either on the iOS devices or using one of them as a personal base station.

When I have a chance, I'll try the iPhone and iPad on either a decent T-Mobile signal or another Wi-Fi network.

New tidbit: from Safari, I get great download speed for the 10.10.5 Combo Updater, so it appears to depend on exactly what kind of transfer is being initiated from what specific app. Music, app store, etc. are all slow for Apple, but Safari seems to be okay even for Apple downloads.

(I'm already on 10.10.5, that's just a large file on the Apple site to test download speed...)

Agreed. It'll be interesting to see what I get when I can use the iOS devices on either T-Mobile or another Wi-Fi.

I just downloaded iTunes 12.2.2 in a few minutes via Safari (on the El Capitan public beta), while it would have taken hours (if it even finished) via App Store. With Safari, I got over 1 MB/sec (reported by Safari, Activity Monitor showed an even higher bitrate), while App Store was getting more like 50-100 KB/sec. All on my Mac, of course.

I'm in Colorado. For me, iTunes Radio is also affected, but as noted in the original post iHeartRadio is not. Unfortunately there aren't many situations in which a Safari download will work when App Store doesn't, but when a non-App Store option is available try it!

And, later, downloading iTunes12.2.2 from support.apple.com via Safari finished in a few minutes, showing more than 1 MB/sec (in Safari; Activity Monitor showed a higher bitrate, probably including the TCP wrappers around the actual data), while App Store Updates was showing only 50-100 KB/sec in Activity Monitor.

A quick test of Music Radio on my iPhone using T-Mobile had no dropouts.

And, using the iPhone as a personal base station (weak but usable T-Mobile today), on my Mac Mini iTunes Radio still stutters uncontrollably, while iHeartRadio is fine.