Macbook Pro (early 2011) lagging, fan spinning, kernel_task taking over

The end of the report has two mentions of memory so perhaps you have loose or bad memory, or a bad memory slot. Try reseating the memory. When inserting the memory nearest the Bottom Case it can make the other module pop loose. Plus the memory slot nearest the Bottom Case can fail due to cracked solder joints from years of pressure exerted on the base of the memory slot/Logic Board. When you have the cracked solder joints just putting pressure on the black base of the memory slot will cause the laptop to freeze and/or get graphical glitches.

Another possibility is the SSD may need a firmware update or the SSD may be failing or needs to be reset to factory defaults. To check the health of the SSD run DriveDx and post the report here using the "Additional Text" icon which looks like a piece of paper. To reset the SSD to factory reset requires a bootable Linux drive and utility to access the SSD's built-in hardware secure erase feature. I can provide instructions if necessary.

Another possibility is the hard drive SATA Cable is bad. You can test this theory by removing the SSD and booting the SSD externally using a USB to SATA Adapter, drive dock, or enclosure. If you don't have the problem with the SSD booting externally, then the internal cable is likely at fault. You can try reseating the cable to the Logic Board in case it has become loose.

When you performed the clean install of macOS did you first erase the whole physical drive as opposed to just the Macintosh HD volume? Unfortunately Disk Utility hides the physical drive from view beginning with macOS 10.13. Within Disk Utility click "View" and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility.