Ummmm....

In that list of things you don't mention "Retrimmed elevator for level flight at 3/4 throttle".

Sorry if this seems too obvious but sometimes it's the simple things that get us.

You may want to try using dive test method to set the balance like the glider guys do. Perform the testing at idle so it's the decalage and balance setup rather than the thrust alignment that you're testing.

Do a google.com on "glider dive test" and you'll get lots of sites that explain it in differenty ways.