Chosen Solution
I just replaced my whole upper case on my MacBook and it has been unbearably slow ever since. I made sure I followed the guide properly and I also cleaned out and reapplied my thermal compound for my CPU. I also mounted the heatsink tightly so it has enough pressure. I have tried doing a clean install of macOS (full drive wipe), resetting the NVRAM, PRAM, and SMC but there’s still a lot of lag constantly. There would be around 8-10 seconds of lag between keystrokes or starting Safari. GeekBench 4 results for my CPU are: 415 Single core and 1396 multi core, which is way less than the average according to the comparison chart. Third-party softwares are telling my that my battery health is at 97% and that my temps for CPU and all other internal components are below 34 degrees Celsius. What could it be?
Let us know how it reacts to running in Safe Mode. Boot up holding down the Shift key. What Mac OS X are you running? How free space do you have on your storage drive?
