Jerks in games at normal fps

CPU - Intel Xeon e3 1231v3 (hypertrading and turbo boost enabled)
RAM - DDR3 CRUCIAL BALLISTIX (2X4GB) 1600MHZ
Mother - ASrock b85 Pro4
HDD - wd1003fzex 1TB
PSU - Corsair VS550 (550watt)
Vidyuha - AMD R9 270B Directcu II OC (2 the video processor is overclocked up to 1000 MHZ, but the problem is relevant even with the
standard 975MHZ).

A week ago I assembled this computer (except for railway, vidyuhi and bp - they are already a year old) and decided to test it in games.
In some of them, such as Metro 2033 REDUX, Dying Light, GTA IV, GTA V, with a decent fps (60-70)
, sometimes incomprehensible jerks occur . FPS during these jerks can drop by 2-3 or 4-6 frames for a split second and
return to its previous state.

I monitored the system and this is what I found ... In the same GTA V, where jerks sometimes occur
while driving around the city, the processor is loaded with a maximum of 55-60 percent, the video card is generally 60-70, the video memory is hardly full:
1-1, 2GB out of 2GB, the temperature of the card in all games, including GTA V, is a maximum of 62 degrees, the RAM is filled in the
same GTA V by a maximum of 7GB.

At the same time, I have a boxed cooler and it doesn't do its job very well. In GTA V, temperatures are
the highest I've seen in games so far - around 75-85. In Dying Light, Metro 2033 REDUX, GTA San Andreas, etc. the temperature of the probe is already in the region of 55-65. At the same time, only in Dying Light, during jerks, I noticed a drop in the processor frequency (apparently just
due to overheating), in other games I did not find a drop in frequency with jerks.

Tell me what could be the problem? Could it be that MSI Afterburner, which I use to monitor the system in
games, is sinning and does not always and not in all games show me the real frequency of the processor, especially during jerks. Maybe the
problem lies elsewhere?
I don’t know if this is important, but ... I have a rather old monitor with a resolution of 1024x768 and it only uses a VGA connector,
despite the fact that the video card needs DVI and I use an adapter.
I heard that because of this, someone had problems with the image in games or somewhere else ... but what kind of problems I do not
know, and whether this is really so.