Quick question on NGINX cache

[J.R.]

> And the main page caches OK, but any page the resides on the "?page_id" is
> not getting cached.  Is there more to the "try_files" that needs applied
> for caching of these permalinks?

Can you be more specific? Which "cache"? Browser cache? Nginx content
cache? try_files has nothing to do with caching...

Either way, you need to check your headers to ensure that they allow
caching for said pages. Also if any cookies are being sent then nginx
won't cache the page.