Matt if you plan on keep the 80 get a FSM that will walk you through all that stuff, also get the supplement Electrical manual. As for meters one with the Volts and the Ohms is the basic. Anything else if you do not know you may not want to know.
So with the VO meter on Volts, hook it to the battery. Read the volts with the truck off. Should be around 12.3-12.7 V. With the vechicle in idle should ve in the high 12(12.7 or so) to low 13. With it reved to about 1800-2000 should be in the 14-14.5V. So next is to turn on everything that draws current. Both at idle and at high idle (18-2000). It may come down but not much from the before recorded spec's. After turning off stuff and allowing the idle to come down, turn off vechicle and see what the voltage is and watch if it goes down fast or not at all.
If your alt is with in these ranges all is fine with it, then check your battery. I have found this to be more of a problem in toyotas then the alt.
Or do as the other matt says, take it in to see what is up. later robbie