Cooling
Do you have any restictions to air flow in front of the radiator?
Air conditioning coils or trans oil cooler coils in front of radiator will reduce clean air flow thru radiator.
Fans on back side of radiator pulling air thru, not on front pushing air?
What pressure radiator cap?
Losing any coollant to recovery tank?
Antifreeze or straight H2O? Water wetter?