When you do the compression test, if the #4 cylinder is way lower than the other three you can determine if it's rings or a valve sealing surface issue. Check the compression reading, note it, remove the compression gauge, squirt some clean motor oil in the spark plug hole and reinsert the compression gauge and check it again. If the reading goes up the rings are the issue. If the reading doesn't go up it's a valve issue. Works, used that procedure a few times over the years.
Hey buddy. I live in Richmond Virginia also. I have a 2011 3.8 track. In reading your thread I'm not convinced your engine is done. What shop did you take it to? I've got a couple good shops that I use for stuff that I don't want to do myself.