I've been trying to figure this out on my own for over a week now and have exhausted my limited knowledge of mac diagnostics... hopefully someone can shed some light on what is going on.

my late 2007 macbookpro, running 10.6, has been consistently freezing on boot and sleep. When booting it freezes at the gray screen with the apple and spinning loader. If I zap the PRAM it boots up fine for that time, but otherwise freezes every time.
It will also freeze when returning from sleep after shutting the lid. The login screen comes back up but then neither the mouse or keyboard will respond and I am forced to hard shutdown. If I simply put it into sleep with the lid open it responds fine; it is only when opening the lid back up that it stops responding.

So far I have replaced the RAM, zapped the PRAM, reset the SMC, messed with the energy saver controls, repaired disk permissions, and ran countless maintenance scripts( be it by hand or automated via onyx and applejack). I have run out of ideas short of doing a clean wipe and install, which I would really rather not have to go through. Does anyone have any idea what could be going on?