Same problem here - TNT2 and 5336 = BAD
I had a working TNT2 installation with the 4496 drivers on Fedora Core 1. I upgraded to the 5336 driver, and glxgears dropped from about 650fps to 60fps. Switched back to the 4496 driver and it's back at 650fps. There's no problem indicated in the log (GLX initialized), but it's not working on the 5336 drivers. Staying with 4496 for now on that machine....