I upgraded the RAM for my old, mid 2009 MacBook Pro.
As I couldn't find 1066 MHz RAM, I bought two 4GB DDR 1333 MHz RAM modules. They are recognized by the MacBook, but it didn't work well and the MBP was slow sometimes. However, when I just replaced 1 RAM module, the machine worked really fine with RAM speeds at 1066 MHz.
Is it possible to adjust the RAM speed?