Highway heat

4.10 gears & hi stall c'ter doesn't make for a cool running engine. Also, the engine produces twice as many heat producing power strokes at 60 mph than it does at 30 mph......but the same amount of coolant has to dissipate the extra heat.
Your elec fans are probably acting as baffles at higher speeds, & temp goes up.
There was nothing wrong with the factory clutch fan & a good shroud.....