iMac running slow with SSD and HDD
I am new to this forum but I cant seem to come right with my issue. I have done a fair bit of research but cant seem to come right.
I have two 27” iMacs, A Late 2013 and a Late 2012 model, both have the same issue. I installed an SSD into the iMac and did a clean OS High Sierra install but the machine “runs slow” if I can put it like that. Anything from opening applications to watching a video takes a while and just seems sluggish. The late 2013 iMac had surge damage but I replaced the power supply and installed an SSD. The Late 2012 model I replaced the HDD for an SSD. After both machines were opened and had the HDD replaced I ran into this issue. I have also tried booting up on an external SSD but have the exact same issue which rules out the SATA cables. I have also remove the SSD from the iMac and used it to boot up on a different machine and it works fine. I am currently just trying to sort out the late 2013 model at this point. I am busy installing Mojave to see if it will make any difference at all but I doubt it as the SSD works perfectly booting externally on a different machine.
Any help would be appreciated here. Its just strange that I have had 2 iMacs at different times with the same issue but I have done SSD upgrades to numerous machines over the years and have had no problems at all.