Overclock my phone but cpu speed drops

Your cpu is overheating because to much vcore you dont need overclock in this cpu slow down... overclock is for professionals...

The most important thing after OC your phone is to UV the processor. Download trickster mode from the Play Store and swipe from the left edge of the screen and go to Specific. There you should find the voltages of the cpu which i will give to you for best performance after Oc(i score 25k+ on antut with those setups on 1920mhz)
CPU: 200 Mhz - 1800 Mhz ( Voltages over 1300 mV@1800 Mhz makes a lot of heat and cpu throttles... )
1920 Mhz- 1350 mV
1800 Mhz - 1250 mV
1704 Mhz - 1225 mV
1600 Mhz - 1150 mV
1500 Mhz - 1125 mV
1400 Mhz - 1075 mV
1300 Mhz - 1025 mV
1200 Mhz - 1000 mV
1100 Mhz - 1000 mV
1000 Mhz - 975 mV
900 Mhz- 950 mV
800 Mhz - 925 mV
700 Mhz - 900 mV
600 Mhz - 875 mV
500 Mhz - 850 mV
400 Mhz - 825 mV
300 Mhz - 800 mV
200 Mhz - 775 mV

GPU: 160 Mhz - 533 Mhz ( Speeds over 533 are useless since making a lot of heat and also gpu throttles... )

160 Mhz - 825 mV
266 Mhz - 875 mV
350 Mhz - 950 mV
440 Mhz - 1000 mV
533 Mhz - 1025 mV
700 Mhz- 1100-1125(depends on the kernel cuz my phone crashes on devil with 1100 mV)
Credits go to @PROTOCHIP as i added only for 1920 Mhz and 700 for the GPU.