Are we talking everquest 1 or 2?
Deleting and repatching is a good step, Also try a drive defragment, check available ssytem memory and hard drive space, maybe look at upgrading your video card drivers. You may want to download and run speedfan http://www.google.com/#hl=en&source=hp&q=speedfan and check the hard drive for physical errors.
It could also be a network issue, is the ping / lag meter showing problems?