Mac Pro

4,1 Mac Pro wont address 1333MHz RAM

Hello all,

I have a 2009 4,1 Mac Pro that I flashed to 5,1. It currently runs the latest boot ROM (, has 1333MHz modules but it won't address them as 1333MHz, it lists the RAM as 1066MHz.

I've reset the PRAM and played around with reseating DIMMs…nothing seems to work. I've looked into the processors and they (2x 2.66GHz X5550 Xeon's) do support 1333MHz RAM (according to Intel). What am I doing wrong?

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