The problem with your theory that nUI must be the problem because it didn't start till then is very strange if you read the link. nUI has a lot of users and if this was an issue caused by nUI don't you think all of us or at least a good portion would be having the problem? I happen to use probably close to 50-75 mods on top of nUI and have never had an issue. Do your self a favor rename your wtf files don't delete them then move your add-ons to a folder on your desktop log into wow with nothing, log out then install nUI and log back in. You wont be losing anything you can put it all back very easily
As a side note I remember hearing something about the wow garbage collector being an issue when in game memory was over 100 mbs. Might that be when your freezing occurs?