I have a 2002 Nissan Xterra with a 3.3L V6 Super Charged engine. I bought the truck used, and ever since I bought it I have been wondering if the super charger is working correctly. My super charger doesn't engage unless I put the pedal all the way to the floor, and even then it's not until almost 5000 RPM. Does this seem normal? If not how can I test it to see if it is working properly? Also, I drive pretty conservatively and I only get about 13.5 MPG, any suggestions on increasing that number?  

Unfortunately, the supercharged 3.3 wasn't one of Nissan's best engines, IMHO. They're not particularly powerful, nor are they very fuel-efficient. If you want to check if the engine's getting boost, I'd do a T-tap into the vacuum line with a gauge, and run the gauge into the cab while you're driving it. Do a few full-throttle runs, and keep an eye on the gauge. Make sure it's within the manufacturer's specs. I think somewhere between 6-8 psi is normal. As long as you're not getting any noticeable detonation, it's probably running normally. An underdrive pulley would probably generate more boost, but probably wouldn't do much for your gas mileage. Don't know what to tell you.