i would like to know where the stock water temp sending unit is. also, if it its not in the most efficient location, would it be smart to use an aftermarket unit, say put the sensor right where the water leaves the engine?

 

stand in front of ur motor. look at ur lower intake, right side in front

 

there are two temperature sensing units on the 5.0 engine, one is in the intake manifold itself just to the front right of the lower intake looking from in front of the car back at the engine. this one is what is attached to the temperature gauge on the dash. the other temperature sending unit is on the other side mounted in the small black metal pipe which runs across the intake toward the heater core. this one is what tells the ECU what the coolant temperature is so it can control the engine.