My carrier is AT&T. It does happen when I connect to Wi-Fi. I've gotten a new router, still the same thing. When I'm on 4G (very slow here as well) it still loads a bit better. I haven't tested it in a better connection area to see if it's just my Wi-Fi, but I'm betting it's my Wi-Fi since I don't believe it's doing it as bad on my slow 4G connection.
I have 100mbps on Time Warner with a surfboard router, and have never had this issue until a few days ago. All speed tests are fine. I've rebooted, powered off, taken the battery out. Deleted and reinstalled the apps, cleared cache in the apps affected as well. Also, YouTube won't load now either on the browser. So I'm believing it's a weird issue going on. It's not doing this on my Alienware, iPad, iPhone on my Wi-Fi, only my Note 3.
Edit: I have confirmed everything is working on LTE as I got a random signal (which I hardly ever get at home, it switched back to 4G and keep it on LTE). This phone would be SO much more tolerable to use on my Wi-Fi connection.