One problem related to o2 sensor has been reported for the 2004 GMC Envoy. The most recently reported issues are listed below.
Bought new and loved the ride. List price was over $42,000. Well maintained. 1st lost speedometer and other gages. Replaced instrument cluster. 40k miles replaced blower motor. 60k miles window behind backseat just dropped. Replaced regulator (I think). 62k miles check engine light - replaced fuel cap then took to dealer - $600 replaced a oxygen sensors. Check engine light came back on a few days later with same code. Just driving with it now. 68k miles - replaced power steering pump. 89k miles - driver side power window module burnt - replaced. 91k miles - while replacing driver side headlight found wire to light was melted. 98k miles rear speakers quite working. Probably a couple of things I have forgotten. 8-12-14 it has 99360 miles on it and still love the ride but have lost faith in gm. I have had 7 gm vehicles and will have no more after this one. Some of these items have had a recall but not for this vehicle even though the same parts are in this one as the recalled vehicles.