There's 2 devices,one is the "Map" sensor which faces up and is towards the pass side of the intake,the other 1 is for the SRV / Short Runner Valve and is more towards the middle of the manifold. I'm guessing you might be referring to the SRV,it switches the manifold from long runners to short runners roughly about 4800/4900 rpm. Your truck has what's commonly referred to as a "dual" runner intake manifold,and the SRV controls the flap inside the manifold that switches it from long to short runners. The truck utilizes the long runners down low in the rpm band to create torque,and then switches to short runners to promote higher rpm horsepower