Bobby 3/22/2010Ross, not sure if i can help with all problems, looked into Envoy speedometer and it appears there is some info on people having this problem and it being due to wiring to the cluster. But before you check that I would say check the speed sensor. People that had the instrument cluster problem were experiencing other problems like warning lights coming on along with the speedometer working erratic.
If your rear speakers aren't working they have possible blown out, or if there is an amp maybe the amp has blown. Test for pwer going to the speakers when the music is on. If there is power there then the speakers are probably bad. Did they four wheel drive not engage just once and then work or is it no longer engaging at all?