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Just be patient. The Cydia servers are still getting slammed with users trying to download stuff.

I'm having no problem searching for apps and tweaks but installing them is another story.
 
Go into your Changes tab and tap Refresh at the top left. Keep doing that until the packages download completely. Yesterday it took me several attempts to get everything downloaded properly. I kept getting errors. Eventually, I got a little thing saying "Reloading Data" in the middle of my screen and everything was updated.


Just keep trying, Cydia's servers are still getting hammered, and probably will throughout the rest of the holiday weekend.
 
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