60mph should be plenty of air flow for an adequate cooling system to keep temps in check. With a narrowed single 1" core aluminum rad, twin 14" fans only came on after coming to a stop, or in extended low speed, or stop-n-go traffic. And would bring temps down at a stop far enough to shut them off. If your fans were running at 60mph, were they running all the time stopped and speeds slower?

 

Sorry, before adding the fans, I would overheat unless I was going 60 mph+. Way over heat at slower speeds or at stops.

After adding fans, no overheating at all -- slow speeds and stop-and-go traffic were fine.

I don't believe the fans were running at ~60mph+, but if I were just running about town even at 40 mph, when I stop, at least one fan will be running.