Q: Mac 10.9.4 is running really slow?

1. Back up your Mac, since what you describe may presage an impending hard disk failure. To learn how to do that read Mac Basics: Time Machine backs up your Mac.
2. Determine if the problems also occur in "Safe Mode":

• Safe Mode or "Safe Boot" is a troubleshooting mode that bypasses all third party system extensions and loads only required system components. Read about it: Starting up in Safe Mode
• You must disable FileVault before you can start your Mac in Safe Mode.
• Starting your Mac in Safe Mode will take longer than usual, graphics will not render smoothly, audio is disabled on some Macs, and some programs (iTunes for example) may not work at all.
• Merely starting your Mac in Safe Mode is not intended to resolve the problem, it's to observe its performance without certain additional components.
• To end Safe Mode restart your Mac normally. Shutdown will take longer as well.

Need some background info like

1. What Mac it is?
2. How much RAM?
3. How big is drive?
4. How much space left?
5. From which OS X you upgrade to Mavericks

Mavericks is slower at times, try upgrading to 10.9.5 as it has resolved earlier bugs.

Etresoft, a long time contributor to these forums has written a program that gives us an insight into what may be wrong with your computer. Visit his site here

Download and report the findings back here.

Pete

It only displays OS X information? Right?

What else it does?

Shows a lot of System Information and what programs are loaded. Download it and run it - that will show you.

Activity Monitor - Mavericks

Activity Monitor in Mavericks has significant changes

Performance Guide

Why is my computer slow

Why your Mac runs slower than it should

Slow Mac After Mavericks

Things you can do to resolve slowdowns  see post by Kappy