We are in Phoenix so can relate to a hot summer day. Just a couple of tricks to add to some of the great ones already tried.
Adding an
oil cooler does help even if
oil is not overheating, add a deflector plate behind the
oil cooler so airflow from the cooler goes down and not through the rad. In theory the cooler would seem to block a bit of airflow to the rad. but it helps. The air diverter plate keeps the load off the radiator.
Shroud or no shroud ? On a couple of cars where I questioned the shroud might be blocking hi way air I added shroud mud flaps. I cut a couple 5 inch round holes in the shroud and hung a square flap of rubber fastened only on the top. I thought air flow or pressure at hi way speed would push flapper open. If in stop n go traffic the flap would allow fan to pull flap closed.