Jeff,
Feel for you on the head gasket failure.
More than the head gasket part numbers were changed at the same time... this doesn't necessarily mean something was redesigned, more likely a supplier changed for some other non technical reason. It could be because this would have been about the time they decided to use the 1GR-FE in the soon to be released FJ Cruiser as well and the previous supplier couldn't meet demand and their lead time was too long. It could also be they found a lower cost supplier.... lots of non-technical procurement reasons a part number would change....
like you, I am an engineer and so the numbers on this issue make me curious...For that reason I created this thread:
http://www.toyota-4runner.org/4th-ge...%2A%2A%2A.html about this issue.
do you care to supply the other info on your failure? if so just reply to the above thread...