I was having major lag issues on my ps3 with this game, so I tried rebuilding the database and restoring file system on my ps3, then deleting the gta v installation and then re-installing it. And it has completely fixed the problem and I am getting a smooth 25-30 fps now.Just google how to do it, it easy very and only takes minutes, and doesn't delete your data.
I dont really play on consoles anymore, but 25 - 30 fps? That's not that good. It might be normal for consoles, but damn i wouldnt be able to enjoy that. A game has to be +35 fps to be enjoyable IMHO.