Stepping 3 and Revision C0
Asus Z87-A motherboard, BIOS '2103'; low power states enabled
The processor used to use the entire multiplier range of 8 to 39 (799MHz to 3.9GHz). Now, at 0% CPU usage it will hold at multiplier 37 and go no lower.
Any suggestions on what to check?
Found the issue was nothing with the processor or motherboard. Windows 7 had changed the power option from Balanced to High Performance. Problem resolved after putting it back to Balanced.