now that you mention it, it would be hard to document that you actually cleaned the EGR. I mean all you need is a can of carb cleaner.
Interesting, someone should call isuzu and ask about it. I DO know that they are ok with you changing your oil as long as you have receipts to prove it.
Oh and in my extensive experience with the 4L30E, the light starts flashing when either the fluid is to low and it starts overheating (although theres supposed to be an trans overheat light for that) or when there are electrical issues in the vehicle. Ever messed with the alternator? Aftermarket stereo?