Those 150 temps only apply to the first and maybe second gen expeditions. Anything with the 6 speed is designed to run at around 200 for everyday driving. They use a full synthetic fluid and the internals are different as well. The 6 speed is thermostatically (mechanically, not viscosity based) controlled and will not allow fluid to enter the cooler until around 185-190. A huge cooler on the 6 speed will keep you at the factory temp under a heavy load but it will not allow you to run any cooler.