I would contact Dell, but I don't think this is a hardware problem. I found a thread on these forums about a different Dell monitor having the same issue but hooked up to an ATI video card. They solved the issue with a setting in the ATI control panel. EVGA (the maker of my Nvidia video card) even has a solution for this problem in their knowledge base and think it is a timing issue. Their fix (creating a custom resolution and changing one setting) is failing though (the test it runs fails) so I can't even try that.
I would hate to send back a monitor without any dead pixels to get a refurb with dead pixels and still have the same problem. I really believe after some reading that it is a high resolution LCD/video card/driver issue.