Windows 7 recognizing 100% of my RAM some places, not others

Windows 7 recognizing 100% of my RAM some places, not others

Before you go blaming it on a 32-bit OS, I'm running Windows 7 64-bit. I have 4x 1GB sticks of RAM installed. I recently RMA'd one stick and installed the replacement. It would seem that parts of my system are recognizing it and others aren't. Both System Properties and dxdiag show the full 4GB, but task manager and rainmeter are only reporting 3GB. What's numbers should I trust and how can I fix this?