That's on the loose side for sure. It all depends on if they're GM gears (5 or 2 cut) or aftermarket. The newer style GM gears like to run tighter. I would use the manufacturer's specs on aftermarket gears.

The reason I said 0.009" was loose for new gears is because of the wear in you experienced....so they'd end up in spec. I doubt you'll gain any more backlash after 500 miles. I like to keep them under 0.008" but others might have a different idea.