I have purchased a 2003 Avalanche and at 65000 miles while driving down the road third gear went out. At first I thought that it might be an electrical failure of the transmission solenoid.

When I took it to the gm dealer I had to have my transmission replaced. After talking to several Gm owners I found three that had the same problem. From what I understand the sun gear lets go and guts the transmission. GM has a problem and they are not addressing it. They would rather pass the cost over to the consumer and forget about it.