Over on the Corvette restorers page there was a thread about the same thing. Came down to part number 12377985. Went down to the local GM dealear yesterday and ordered some.
Came in today and it's labeled 'Chassis Grease'. Further reading says " GMC CHASSIS GREASE is a premium grease for chassis lubrication. It is made up of a special grease consisting of oil, lithium thickening agents and special lubricants. This product is standard chassis lubrication on all GM vehicles."
Sounds like pretty 'special' stuff to me.
