People usually during upgrading just take the old hardware out and plug the new hardware in, without uninstalling anything beforehand. Usually, that works out OK, but GTAIV likes to pick up on everything.
If that's your case, it would be advisable to completely uninstall the nvidia driver package, reboot and install a fresh batch from their site.
Additionally, the benchmark tool is broken and you should ignore it completely.
Second thing you'll want to do is to disable the SLI for GTAIV as it can only give you problems and no performance benefits.