I used a replacement of the resident.rpf with a 80k siren:

I can listen to the tones in openiv and it points to the correct path (/mods/x64/.../sound) but for some reason in game they revert back to the vanilla shitty sirens
All my vehicles are ELS. What am I doing wrong?

Replace the Resident.rpf in the main Grand Theft Auto V\x64\audio\sfx path not the mods folder if you're trying to use it with FiveM 

1 hour ago, bakerxgooty said:

Replace the Resident.rpf in the main Grand Theft Auto V\x64\audio\sfx path not the mods folder if you're trying to use it with FiveM 

Sorry, I am trying to use it with GTA5 story mode/LSPDFR?

 

I dragged and dropped it to RESIDENT.RPF in edit mode and in the mods folder but it refuses to use the siren.

You need to replace the resident.rpf in the mods folder for that to work. It should be as simple as dragging and dropping