I’m up to date with OS 10.13.3. Since 10.12+ I’ve been bothered by the beach ball intermittently appearing when internet pages load and slow startup of Word, Excel and Safari. My ram always seems to have at least 3 gig available.
½ of my hard disk is empty so a full disk is not the issue.
“Quick look satellite” frequently takes up 90% of my CPU when things are loading closely followed by Activity Monitor at 6 to 9%.