Why does itunes freeze whenever I try to sync an ipod?

Lately I've been having this problem with all of my Apple devices. Whenever I connect one to sync to my iTunes library, the program enters the "verifying" or "selecting tracks to sync" phase and then either grinds to an extremely slow halt or stops completely. This has happened with my old iPod classic, my iPhone, and now a brand-new iPod classic that is fresh out of the box. Did something go wrong with an update to the iTunes program? Right now, I've tried reinstalling iTunes and reformatting one of the iPods, but neither approach had any success. What else should I try?