Frequent freeze up of early 2009 Mac Pro

Here’s some follow up: With one 8GB OWC RAM in slot 1 and another 8GB OWC RAM in slot 5 the MacPro ran for almost 3 hours and then froze up again as before. BUT I then removed the RAM in slot 5 and put it in slot 2. On start up I got a message that this wasn’t the optimal placement of the RAM. But I proceeded anyway. My computer has been humming along blissfully now for just over 6 hours. This is the first time it has run this long without freezing, so I am optimistic. If it is still running in the morning when I wake up I think the problem is solved. For my purposes I can get along with 16GB RAM. I’m beginning to wonder if the problem is with one of the slots rather than the RAM itself. I believe I’ve read somewhere that this can happen. Thanks again for your help.

Grant, Thanks for your knowledgeable and prompt reply. I was suspicious that RAM might be the problem. But Techtool Pro said the RAM checked out fine. I have 8 RAM sticks in all from two different sources. I trust the OWC memory more than the other. So I am now testing with two 8GB RAM modules from OWC and leaving the other slots empty. It is hard to know for sure the best RAM configuration in the Max Pro when using two modules of the same size. For now I used slots 1 and 5. I’ve been up and running for over an hour now with no problems. Keeping my fingers crossed. (But here again, I’m not sure which fingers I sure be crossing. )