I have been having this ongoing problem and have taken my vehicle into the Chevy dealer in Olathe Ks Ive been told it was the spark plugs-had them changed didn't fix it I have been told different things. This last time I was told that I need to put it into 2 wheel drive and keep it there even though when I purchased the vehicle I was told to put into the Auto mode. So I did what they said and I barely made it home with the truck. Very frustrated! and to make matters worse my 2 brothers bought the exact same type truck on the exact same day as I did and we all three have the exact same troubles. What is going on? I was also told that Something else could be the problem that would require me to pay almost $9000.00 for a truck that I bought new 4 years ago but for now they said the 2 wheel drive thing would fix it so I think I'm in serious trouble because I can't afford to fix this 4 year old truck. This truck does have some smoke sometimes but its pretty scary to drive especially in fast traffic.