i have one sitting on the shelf in the garage for my 99 3.4l right now, never installed, bought brand new from urd. i still have a question or two of my own which will help explain why i never installed it. the units are supposed to give you about 15 hp, but my biggest concern is what happens to the fuel economy, i would love to know that. here is my biggest beef with the unit and urd; they never tell you how labor intensive the process is to tune it before you buy it and never explicitly tell you all you will need tools wise to do so, it wasn't until the unit got to my door and i read the install instructions that i learned i needed an air/fuel gauge/reader, another $350 (the unit alone is less than $300). to hook it up you need to weld in an exhaust bung in your down-pipe before the cat, requiring you either weld it yourself (luckily i own a miller mig) or take it to a shop. i bought the obd 2 scanner at the same time, which is a good thing, since you need it too. you need to essentially remap your fuel curve using the air/fuel reader to get you the right mixture, and the obd 2 scanner to make sure you're not throwing any codes and able to read the diagnostics, all the while driving the truck. if you plan to tune it yourself, you will most likely need the help of a buddy. here is a little light reading to let you know what you are in for.
http://www.gadgetonline.com/U-Tune.pdf if you are interested, i would entertain the idea of selling mine for a savings of what you'd pay from urd.