I have a 2008 MBP and I upgraded it with a 960 EVO 1 TB SSD and 16GB RAM a couple years ago. Performed like a champ up until a month or so ago. It started operating really slow and freezing up randomly. I ran a first aid and it showed a problem with some kind of catalog, I forgot what it was called. I did a network reinstall of High Sierra and it look 26 hours. When I went to test it, everything was the same. All my files were there, preferences, none of the stuff you do when you clean install macOS. Moving the pointer is very laggy and trying to open anything was severely laggy. I'd click on Safari and wait literally 2 minutes for it to open. I finally managed to download macOS and created a bootable USB. From setup, I erased the SSD and reinstalled macOS. After about 3 hours last night with it at like 25%, I went to bed. I got up this morning and was at the iCloud setup and completed installation. Everything is still extremely slow. Just moving the pointer alone is very laggy. Trying to open any folders or anything has sever lag. I ran another first aid and it found no errors. Does this sound like I need to replace the SSD? I was thinking about trying to install macOS to external drive I have and see how things run.