Hey guys, weird question. Hopefully someone has the answer. I have a 2009 Mac Pro. 8 Core (8 RAM slots). Had 8 x 2GB sticks of RAM in it (16GB of 1066MHz RAM). Installed 32GB RAM, in proper order, and came out to be 4 sticks of 8GB. 1066MHz. Installed the next 32GB RAM, for total of 64GB RAM. RAM downgrades itself to 800MHz speed. I remove slots 4 and 8, and the computer has 48GB RAM. Runs at 1066MHz. It looks like slots 4 and 8 either have an issue, or doesn't like lots of RAM. I have no idea why. I tried various configurations and it looks like the RAM is not at fault, but something with the configuration of RAM + board, because it didn't do this with the 2GB sticks, nor did it do it with the RAM jumbled up. The RAM is micron RAM, purchased from 1-800-4MEMORY, which is supposed to be a good supplier, and have been VERY helpful so far in tracking down the issue. It is half-height desktop RAM. Very weird, since I've never seen any RAM cut like that. Anyway, if anyone has ANY idea of what is going on, please chime in. Thank you for your time.