Quick summary: Monumental effort to upgrade DNN site from 4.5.3 to latest 5.6.2.  First part of project was upgrading site to 5.6.2.  The second part was to move from development to test (pre-production) servers using a gateway (site's IP address is exposed, but talks to its database through a gateway [a mirror of the database and stored procs] - the database itself is behind a firewall, a 3rd-party is hosting the test site and has configured the gateway themselves).

After 3-4 weeks of effort, all finally seems well except for one thing - when logged into the site, the HTML module (editor) displays different content depending when in view or edit modes.  When in view mode (or when logged out of the site and viewing as a normal user), the editor displays "old" content.  When logged in as an admin and site in edit mode, the editor displays "new" content.

I've read other posts similar to our issue:
http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/108/postid/182867/scope/posts/Default.aspx
http://www.dotnetnuke.com/Resources/Forums/tabid/795/forumid/108/threadid/166434/scope/posts/threadpage/2/Default.aspx

The 2nd post seems to have a solution that describes a "Design" option under Page Functions (upper-left of page), but that doesn't exist with latest version of DNN.  I've also considered this a caching issue, but I am not convinced that it is.  During the first part (before gateway), there was no issue - updated content always visible no matter what, problem became apparent after site configured with gateway (which makes me think the site somehow gets wrong data when in view or normal mode, but that really seems far fetched as everything else seems OK).  Yes, I double-checked the Workflow, it's set to Direct Publish.

I will try to create a new admin, maybe existing accounts have been corrupted in a way that prevent their updates from showing correctly.  If there are others who have encountered and importantly have resolved this issue, I would be very grateful to hear form them!

Here's an update - ISSUE APPEARS RESOLVED...

The 3rd party IT folks said problem fixed after moving site to another server since the server was also hosting the production version of the DNN site (albeit the older DNN 4.5.3 version).  Although not 100% sure, they thought perhaps the two DNN sites somehow were sharing resources in such a way that the updated site kept serving a cached version of the home page with the older content from the older site.  The specifics are unknown as to what resources they may have been sharing.

A day later, they informed me they actually resolved the problem with the upgraded site hosted on the same server as the production site.  Again, the exact specifics are not known, but they mentioned clearing out the temporary ASP.NET files and performing, if I remember right, an IISRESET to clear out any cached data in memory (and maybe also restarting the app).

In conclusion, the actual cause of the problem is not known.  But, it appears this was a caching issue pertaining to the server and IIS, and not DNN's page caching feature.