Here's something to try.
It won't "disturb" anything if it doesn't work.
Do this:
- open the "users & groups" preference pane
- click the lock icon and enter your password
- now, click the "+" sign (above the lock icon) to create a NEW account
- create a new, "temporary" account with an easy-to-remember name and password. Give it administrative privileges.
- now, LOG OUT of your "regular" account, and log into the new account.
Do the problems persist?
Or... do they disappear?
If the Mac suddenly starts running better in the new account, then something in your regular account is mucking things up.
If the problems persist, then you know it's not related to your account, but to something else.
Give this a try, takes only a couple of minutes.
When you're done with the temporary account, just delete it.