GPU sags during games, what is its reason?

Question

GPGPU

Intel core i5 2500k Sande B
ASUS P8P67 LE
Gigabyte GTX 760 4gb
SSD 120GB ( System)
HDD 1TB
8GB DDR III 1600 Kingston HyperX
PSU Corsair 850W
Greetings, friends!
My story is very rare and happened to one in a thousand people. I found two topics on the net with a similar problem, and alas, on the forums, all the action was cut short in half. There was no solution. I haven't found a universal answer for this. And now directly to my tragedy.
2 years ago I bought a GTX 760 to celebrate the release of Battlefield 4 to replace the HD 6970 Toxic. There was no joy. Played at ultra-settings (60fps) in Battlefield 4. Played for about three months. Then I didn’t play for a month, and when I turned it on, with the same settings, the FPS significantly sagged. This has affected all games. Both old and new. I began to look and measure. And I noticed in GPU-Z That the GPU load is not stable! It jumps often and cannot load up to 99%. It happened that it simply and constantly jumps from 78 - 89%. During such drawdowns, FPS drops wildly in the game, in any game.
What I did and of course it didn’t help me:
I cleaned the computer from dust, including the vidyukha (I already had a clean system unit, but still)
I demolished Windows (Windows was installed with front 7) I changed the
thermal paste on the process
Ставил 8-ку, 8.1, сейчас 10-ка.
Докупал SSD
Касперским вдоль и поперёк обшмонал всю систему, ничего не нашёл.
Собственно ужс! Я бы уже бросил это дело, купил бы себе новую мать, с процем и видюхой но грянули санкции и теперь одна только видюха за 30к. Помогите други! Надеюсь у вас была такая же проблема и вы её решили! Поделитесь же её со мной. Я в отчаяньи и у меня дикая хандра. Скрин прилагаю ( по поводу проседаний фпс)

Answer 1

Проверь аидой под нагрузкой. Троттлит - нет?

Answer 2

В этом и соль что искусственные тесты проходят на ура. Хотя в фурмарке выдавал 15фпс