One problem related to transmission gear slipping has been reported for the 2005 GMC Envoy. The most recently reported issues are listed below.
6/13/2011 vehicle taken to GMC service for transmission flush and filter change. Returning home same afternoon vehicle transmission started slipping and stopped moving. After repeated attempts to move vehicle it was towed to local dealership. Service manager stated that probably broken hard parts inside the transmission were to blame. Rebuild trans. In range of 2$k, replacement $3k. Spoke with GMC coustomer service, no explanation why transmission failed or assist to repoace transmission. This vehicle has 105,151 miles on odometer.