4870x2 problem in gta IV

ok so before i got rid of my micro stutter but now i noticed to no matter what resolution or graphic settings i put, itll run about 20-30 fps outside and 60fps when im in a room in the game, i find this to be wierd is this a normal problem or is it unusual?4870x2 problem in gta IV
Games normally run faster when you are in a small enviroment like a room compared to being outside (there is a lot less going on in a room than a busy street with cars and pedestrians). Also your not getting much FPS because GTAIV is a realllllly bad port thus pretty much nobody can max it really well.