Jeff..Let us say..good post.
Apparently you guys have done your homework, right down to the beer drinking part.
There is no way to read codes unless you take it to a dealer or you know of someone with a Tech2 scantool.
Best schematic and diagnosing (which would include using a tech2) would be from the factory service manuals which are typically produced by Helm. They can be found on Ebay usually at reasonable prices. Or possibly there is a member local to you with them. The diagnosis is probably too many pages to scan.
Probably not a blend door itself issue as much as a airmix door actuator aka blend door motor that sits on top of the programmer unit you switched out. You do remember plugging that little motor in right?