I have had this issue for months.
I did fix it by running the game in windows xp sp 2 compatibility mode. That worked for some time, then the low fps came back.
Then I read another thread that said to install a certain version of directx. This did fix it for a long time, but its back randomly.
I've reinstalled this about 4 times and it fixes it temporarily, then will randomly stutter again. Reinstalling this directx package no long works.
Then I tried another suggestion to use the program dxwnd to run the game. It apparently helps with older dx games. I ran stbc using the default profile and it didn't make any difference.
I've also tried every single NVIDIA control panel setting and nothing worked either.
I'm now at a loss. Tried every single fix from threads dating back years and nothing works anymore. and anytime I did fix it, the low fps would come back randomly. note that I did not change the game files, mods, or install new drivers. It just does it.