bajaexpy, the tranny temp I would consider a must. As for the others, depends on what you are looking at. If you have lots of lights, then a volt meter would be probably most beneficial as it would tell you when you are overloading the alternator (drop of the voltage to under 12.6 VDC). If you are worried about mileage, then a vacuum gauge or one of the "efficiency meters".
For a gas engine, the pyro isn't going to tell you a whole lot. If you were force aspiration, then it might be of a little concern to you. The big thing you need to ask is what are you worried about with the truck and therefore, what numbers do you need to see? once you answer that, the gauges will be easy to figure out.