If I grab the drive line by hand and try to twist it, it feels normal. I
think the backlash on the ring and pinion is good. I looked at the gears
before I installed the third member and they looked perfect. I'm
thinking it has something to do with the sure-grip?? What happens
when the Auburn Gear style sure-grips go bad? Has anyone had any
experience with this?

Thanks
Mike in WA

You will first feel the ring and pinion backlash but if you turn harder, you will over-ride the clutch action (pre-load) and feel the side gear / inner pinion gear backlash.
So put a wrench on the yoke and turn it harder to see if you can feel more free-play.
DD