You'll always get some freezing on boxes and the F5's are very basic, not designed with a lot of power but that said make sure you are connecting via Ethernet for a better result than wi-fi. keep your box up to date too, check your cables etc. There isn't 1 answer for freezing picture, it could be a number of things, just make sure your setup at home is ok.
Also have a read of the loads of freezing issue threads on the forum, you may spot an answer that works for you
Good luck :)