Question cpu high temperature and cpu speed is decreasing

Sep 30, 2020
i bought a dell e6540 laptop since 4 months with ci 7 4810 mq processor and amd gpu 8790 2gb ... it was only reaching 78 degree when i run stress test on cpu and cpu speed always stay at 3.9 ghz because of speed boost no throttling no lag no frame drop . but these days my laptop suddenly changed cpu speed decrease untill reach 0.4 ghz and temperature is 97 degree always fps drop after 5 minutes of playing i changed thermal paste and clean my laptop but the same problem i checked the fan speed it was 3800 rpm and checked the heat sink no any problem till now i don't know what i do with my laptop even i used expensive cooling thermal paste arctic mx -4 no any changes any help please where is my laptop problem . im using xtu to stress cpu . i changed too many windows versions and checked my laptop by dell diagnostic hardware but no changes even i changed the power that reach the cpu by windows 10 power management to 50% the cpu work on 2 ghz but after some time temperature reach 85 and fps drop even im below cpu base speed 2.8 ghz ... im sure someone will give a hand here .
- measured by intel xtu and cpuid - yes i mean that type of cpu (i7 4810MQ CPU ) -stress test by intel xtu and cpuz that stress cpu - 78 c since 2 months - now it is 98c yeah i cleaned it by alchol and tooth paste and by air - i didn't block any cooling in case and i don't know how to do that because my laptop don't support that - yeah i ran it now show me 98 c -yeah i cleaned it by alcohol and it is became like a mirror . - i play gta v - pubg lite - pubg mobile - pro evolution soccer 2017 and call of duty 4 - game setttings medium in all no v-sync - game resoolution 1366*768 and 1920 *1080 and 1280 * 720