My advice: you've got to identify the page or pages that are causing the problem. I've seen no instability w/PHP except for a couple of rare coding constructs that have sent PHP into space. For example, with 4.0.3, I had problems with the sprintf function group, so I constructed my strings manually.
If you can identify which page or pages (try the server logs first) are causing the most trouble, try isolating them in some test scripts.
Dave
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