Bean, Sorry, but I've been very tied up all this season with other issues going on and Pool Forum has had to be back-burnered.

First, what is "shock"? Is it cal-hypo, di-chlor, liquid chlorine?
Second, CYA can take up to a week to show up in measurements. What are you using to test CYA? Not strips, I hope. Strips are virtually useless for that.
Third, on an 18k pool, 2 # of stabilizer when your CYA is 0 is going to do much. 6-8 pounds may actually get you a reading, but, again, you'll need to wait a week.
Fourth, in closing instructions I always suggest you raise and keep FC at shock level--with a CYA of 0, that means 10ppm. CYA from 0-30, the FC should be 12ppm, not the 5.5 you've hit.
Fifth, I'd add 2 gallons of 6% bleach immediately to get your FC to 12ppm.
Sixth, review the stickies here on closing a pool. I've never been one to suggest adding bleach over the winter since I'm in NJ, and it's not necessary here...I've never done it.

Hope this is a start.

Carl