FPS/Lag issues with GTA IV PC Version

I have GTA IV for PC and im running bootcamp with Windows 7 on my MBP 15". My native resolution is 1440x900 and i have really bad lag issues if i try to run the game that high. I dont have issues with most other games, it just seems like its Rockstar games. I have the same issue with L.A. Noire. I have an Intel 3000 HD Graphics Chipset and AMD Radeon 6770M HD Graphics card also. Its an Intel Core i7-2760QM CPU @ 2.40GHZ. 4GB of RAM. Usually i have to drop some setting and resolution to like 1280x720 or so. I can run games like FarCry 3 with virtually no issues so i dont know why i have problems with GTA IV. If anybody knows any tips or tricks, or if theres something im missing or overlooking, please let me know