I'm currently in a conversation with Nvidia tech support. They supplied me a slightly newer "hotfix" version of the driver (dated only two days newer than the one I was using), asked me to do a "clean install" of that driver which I did, and... it didn't fix the problem. Now they're walking me through other setting changes that I've already tried, though I'm humoring them and trying them again anyway under the new driver, just to be sure.