6-month old Mac Pro has already had a new logic board and power supply

Question

At a cost of $400 in shipping and a one-month wait, my 5-month old Mac Pro got a new power supply and logic board
Now I keep getting kernel panics, runaway kernel_task in Activity Monitor, and corrupted boot drives
External Firewire drives work some of the time, and occasionally my USB devices dont work either
This computer is a nightmare - how do I begin to figure out if this is OS (10.6.4) or hardware related?
The extended AHT test reports that all is OK - as does an extended memory test using Applejack
Should I do firmware updates and re-install the 10.6.4 combo pack, or am I just wasting more of my time?
I've got 4 macs and this is the only one that works badly - I think Apple's OS updates are getting as bad as Windows updates

Answer 1

My first question is why you spent $400 to get a 5 month old system fixed. That should have been covered under the warranty. So someone ripped you off, or you left out some key details.
And if you had both the logic board and PSU replaced, did you ever stop to think that maybe the problem lies with the power coming into your house? It's not really the big power spikes or blackouts you need to worry about, since those are pretty rare. What you need to worry about are the small fluctuations in voltage that happen several hundred times a day, if not an hour. Sometimes there's not quite enough power, other times there's a little too much, and all of this takes a steady toll on the PSU. It will do what it can to try and feed the rest of the computer a steady diet of electricity, but sometimes a jolt will get past it and start damaging other components. It could even cause data corruption on your HDD.
If the PSU and logic board already went, who knows what damage it may have caused to anything else. It may just be taking longer to show up.
It might also be that whomever ripped you off to the tune of $400 simply traded you one defective logic board for another. Or maybe they don't really know how to protect against ESD. I once saw a repair shop where the techs smoked in the same room they did the repairs. Sadly, for every one good tech out there, there's probably at least 3 complete idiots. Kind of like auto mechanics.
And I never have problems with Windows or Apple updates. Seems like on Windows the majority of people who have problems with updates are either running some program designed to change the way Windows looks or messes with low level system files, or they have a malware infestation they were unaware of/oblivious to. Most of the people who have problems with Apple updates seem to be the same way. They're running some truly bizarre programs that mess with the system in ways programs were not intended to mess with the system. There's generally a reason OS vendors provide an API for developers. You deviate from that at your own peril.