it looks like you've got all the i's dotted and t's crossed with that set up.
i'd circle back and try another t-stat. maybe the one you got was faulty in some way-- just because it's new doesn't mean it's any good.
from there another possible is that the thermostatic clutch isn't performing correctly, i'd have a look there too.
is it possible that your condenser and trans cooler (if you have one) is somehow limiting the airflow thru the radiator?
have you temped the flow on the radiator with an IR gun to make sure that there's no internal blockages, flow is correct, etc, etc?