New O2 sensor for $19.50
 

I just had to change out an upstream (before cat) O2 sensor. They are only $19.50 with free shipping on eBay. They are by Standard Motor Poducts which is one of the largest OEM manufacturers. The part # is SG1066 and has the OEM connector, not a splice on. After installing I watched it on my scanner and it switches just as fast as the other original one still installed. Excellent quality and good value, so I wanted to pass it on to my fellow Hummer owners. Here are some links to the brand:


http://www.standardbrand.com/Feature...s/Content.aspx

http://www.standardbrand.com/upload/...O2-SENSORS.PDF