There are 12" fans and then there are 12" fans.. I have a Derale dual electric fan set-up on my aluminum radiator. The engine is a mild 454 BBC. I have it wired one relay for each fan. One fan is on a simple on-off switch and the other is on a temperature sensor set to come on at 200 degrees coolant temperature.. I live in East Texas and our temperatures are already hitting 100 degrees.. These days I start the engine, hit the fan switch and drive away.. Regardless of driving conditions, the coolant temperature settles in at 180 degrees and the second fan NEVER comes on. Here's a link to the Derale system.
https://www.summitracing.com/parts/der-16927
You have a severely restricted coolant flow if the engine overheats at highway speeds. Overheating while sitting still and idling means restricted air flow across the radiator, or those fans aren't spinning fast enough or just aren't capable of moving air.