[SS Tim]

That is a good question and one I hope to eventually nail down. But here is a tidbit.
Shown is a mailer dated May 72

--"NEW CHEVY
HIGHANDER
----_SPECIAL.
PRICED
-$260.50 LESS*."

Inside it announced

------"NOW YOU CAN
----------COMBINE
HIGHLANDER LUXURY
-----WITH POPULAR
--FACTORY OPTIONS
------------PRICED
-----$260.50 LESS*."

The back cover also noted
"Your Chevy Dealer is in a national sales contest and he is anxious to give you a great truck deal RIGHT NOW!"

So take away from that what you will but it sure sounds close to if not an inital national release. Plus it also again confirms the Highander was a seperate trim upgrade option that the Promo Package trucks included and were based upon.

Might just have to do a Promo (YG6-8) build date survey thread.