On a hot day running solo my dually runs about 210 - 215 ( stock 454 , 195 deg thermostat , cleaned out rad. , prety new water pump , aux trans + oil cooler and electric fan). With my camper in tow ( 7500 - 8000 lbs ) runing 70 - 75 mph it runs 230 - 240 to close to the red zone for comfort. If I slow down to 60 - 65 it runs 210 - 215 all day long. It has always done this and I havent found anthing to help it run cooler. Do they all do this ? The temp sender is in the head.