I have the same problem since yesterday! YouTube & Pandora won't load, but they work fine on WiFi! It must be the Sprint network problem!
I called and tried a few resets with no luck, I have a pending ticket number 19778227-140314
Ideally, YouTube and Pandora would run better on 4G because they need a higher quality data connection to work reliably. This explains why it works on Wi-Fi. I used Pandora a lot, but had trouble on both 3G and 4G.
Are your settings set to 4glte and not just cdma that allows only 3g.they're easy to find in the network settings
settins>connections>more networks>mobile networks>network mode