If you're having to hold about 1/3 down stick now then that suggests that you went too far forward with the CG. Or at least more forward than you required. Try moving the CG back a little at a time until you only need a slight push of down for inverted flight.

In one of my earlier posts to this thread I described how you can do some dive testing to check for just how pitch stable the model is. Go back and try this as you move the CG back and retrim for level flight. It's a great way to tell just where the model REALLY wants to be balanced and not where someone thinks it should be.