... Yeah. You're getting bottlenecked, dude. Tomb raider is rather CPU-heavy, and that Athlon isn't able to keep up. Just check your usage next time you play.
Which game(s) and at what display resolution?
What is your CPU model and how much system memory do you have installed?
Full system specs, Athlon x4 ii 640 3.2ghz 4gb ddr3 1333mhz Radeon 6670 GDDR5 ( soon to be 7770 ) 500w psu ( crappy one came with a cheap case , concerned my pc isn't getting the juice it needs ) 1440x900 Win 8 64 bit
Getting 40 fps in tomb raider on high settings, then boom , 25 fps in big building zones such as shanty town. ( I do understand others have had these issues and that these areas are quite CPU intensive )
Lower resolutions tend to emphasize/exaggerate a CPU bottleneck.