I have one of these for sale from my 1997 Chevy C1500 5.7L. Wifey and a friend both bought me one for my birthday! You can go here for a run down on it:
http://www.hypertech.com/programmer.html
One of the best features is that you can read the DTC (Diagnostic Trouble Codes) from the ECU if you get a "check engine" light! Also the ability to recalibrate your speedo if you change tires/wheel heights.
$250.00 shipped