Consult the underhood sticker.
The spark plug gap for a GM vortec V6 is .060
.060 in inches.
Consult the underhood sticker. By the way, the last Astro was in the 2005 model year.
That is the rubber boot that is on the end of the spark plug wire that goes onto the spark plug.
A person must leave the right size gap for the spark plugs when changing them. The 1999 Chevy Suburban has a spark plug gap of .060 inches.