Got me a 2011 MacBook Pro refurb from bestbuy mdl A1286 I believe. Replaced the hdd with a 500Gb solid state and also swapped out the memory to 8Gb from 4Gb. That helped non with the issue, but does have good speed when all works. Problem is it seems as if I have to do an SMC reset all the time. It slows to a crawl as if the cpu has been throttled back to the dark ages. Temps look good too. Hardware diagnostics passes everything. Highest I have seen cpu is around 60c, memory 52c, ssd 36c. I do see the kernel is running at 6 hundred something every time it happens. Not sure why, but when I reset SMC the kernel is below 50%. Could it be I need to tear down and redo the thermal paste? Or is this a bug in high Sierra?