Two problems related to transmission noise have been reported for the 2006 Chevrolet Avalanche. The most recently reported issues are listed below.
I backed out of my driveway stopped my truck like always put it in d to drive heard a loud clunk noise and now I have 1 and 2 gear only to use the truck was stationary was on a main road I changed the transmission fluid screens filters everything flushed it out and still the same thing a lot of people are saying it's the sprag unit I have no idea what that is I have only hauled a few things with it when we were moving we only moved eight miles down the road used a trailer and the tow gear that is on the truck. Also about a month before this happened the stability system light came on and said disabled but has not done it since also my truck is very clean always serviced according to the manual and is in very very good condition.
I made a stop, up on taking off my truck made it to second gear and I hear a loud broken noise, transmission went out on second gear.