Image jerks with good FPS (Grand Theft Auto: San Andreas)

In general, I recently encountered a problem, in the sump, the FPS is kept at 40-60, while the picture clearly slows down, as if it hangs for a few milliseconds, but noticeably! As if the image is jerky (again, not very noticeable)!
I have two vidyuhi: 1) gtx 650 1gb | Palit, 2) gt 9600, also a palette, tested both, "image jerks" are still noticeable.
Moreover, the gtx 650 produces a maximum of 60 fps, and the gt 9600 - 100 fps! Weird!
Windu reinstalled, cleans the computer with an antivirus, cleaned it from the inside, transferred everything that was possible! I even turned off all the effects in Windows, the picture still slows down, and goes with slightly noticeable jerks! With normal FPS!
Or memory ..

In general, I think about the processor, because it is already about 7.5 years old.
Here are my components:
1) Monitor Phihlips'24.
2) Video card: Palit GTX 650 1gb.
3) Processor: Intel pentium Dual CPU E2160 1.80GHz.
4) Power supply unit for 450w.
5) RAM: 3gb
6) Win 7 home premium
7) Motherboard: asus p5k-se

In general, that's all, I hope it's about the CPU, thanks in advance for your help!

103 FPS on gt9600, 60 fps on gtx 650.