I cannot tell you what the resistor does I can only assume that it does the same thing as a boost cooler. If your truck has a tuner then most likely it produces more boost then the map sensor of the truck wants to see. What happens with a overboost situation is the truck defuels so it stays within the parameters of the map sensor. The boost fooler tells the map sensor that everything is within the parameters that is should be and now you can make more boost and not refuel at the same time. My opinion is to go with a actual boost fooler not a diode or resistor. I have the one from Dieselsite and I can't say enough about it, give them a call they will set you right up.
in simple terms. if youre truck is making more than 23ish psi of boost then the pcm is defueling and not getting the full potential of what you could do. The boost fooler only lets the pcm see numbers below 23psi. so your truck wont defuel. should make a little more boost and power.