http://www.fallout3nexus.com/downloads/file.php?id=8886 (http://www.gamesas.com/index.php?/topic/1069833-relz-fallout-stutter-remover/page__hl__stutter) may help. It is an offshoot of http://www.gamesas.com/index.php?/topic/1160496-relz-oblivion-stutter-remover-osr/ that SkyRanger-1 made for Oblivion. OSR is critical for a heavily modded OB and it's development is ongoing, however, most people don't see that much improvement with FSR, for a number of reasons such as: FO3 is better codded in the areas that FSR seeks to improve, FO3 has fewer mods. Hence the FSR thread has become somewhat buried...
It's worth a shot trying FSR though. Proper use of it requires that you read the readme and even go through the related threads because it's configuration depends on your comp.
There may be some other things you could do... maybe search the Nexus for things like "simple shaders" or "reduced textures".
Best to describe the components that make up your comp for more help- processor, graphics card, amount of ram, etc.