So a Late 2013 iMac I bought has been having quite severe issues. The hard drive has been replaced with a Toshiba hard drive, so the temperature sensor does not work correctly - therefore setting off the fans. This is corrected with the 'SSD Fan control' but the computer still runs terrible. Worse than a plastic MacBook that I have for comparison. The computer is indexing but that cannot equate to kernel_task taking a supposed 300% of the CPU! Not sure where to go next, as I got the computer at a steal and it is in overall excellent condition. Thanks. EDIT: After removing 'AppleSMCLMU.kext' as well as editing the 'IOPlatformPluginFamily.kext' the computer now functions perfectly.