It will always be difficult to diagnose without having the computer in front of me, but I'll try giving it a go. Have you gone through NVidia inspector and added FalloutMO.exe and FNV4GB.exe to your profile, and set Multi-display/mixed-GPU acceleration: Single display performance mode and set Power Managment Mode: Prefer amximum performance ? Have you tried MultithreadedAI=1? I have found it adds no instability and the author of FNV4GB.exe finds the same. This should help with AI heavy areas Have you tried switching from v2.0a to v3.0 shaders? Open Renderinfo.txt in your my documents\my games\falloutnv\ folder. There will be a line for Shader Package: [Number] Now go to you Data/Shaders/ folder, and renambe shaderpackage[number].sdp to shaderpackage[number].sdp_backup. Make a copy of shaderpackage019.sdp and rename it to shaderpackage[number].sdp In your inis. set bAllow30Shaders=1. When the FPS drops occur is there alot of noise? Have you tried upgrading the Vorbis engine? Also, do you have NVidia Geforce Experience? It has been known to cause issues with certain games including both Fallouts.
Also 2, when you say vanilla, is that still with the utilizties such as 4GB, NVAC, NVSR?
Adonis_VII's post in Awuful performance in New Vegas was marked as the answer