2017 GMC Sierra 5.3 with the 8 speed transmission. Upon cold start up while shifting from 1-2 the transmission clunks real bad. Even after driving and returning from an errand the 1-2 shift will clunk, very noticeable even passengers notice. I do not expect a normal life expectancy from this transmission due to this problem. Brought the truck to a GM dealer, service advisor said "they all do that", no fix. I changed the transmission fluid very early (very expensive fluid change!) as there was talk that a new fluid may help. No difference, still clunks.

I would not buy another modern GM truck after this experience, dealer did not help, many owners complaining of the same thing and more major problems with these trucks is the carbon build-up due to the active fuel management and direct fuel injection along with fuel injector failure, 4WD transfer case sensor failure and fuel level sensor failure.

I bought this truck in Dec. 2017 at the local GMC dealer in Ventura County, went on and garaged for 2 months, then decided to drive to Las Vegas - and that's when I noticed this brand new truck's poor shifting transmission clunky noise when accelerating, and when driving a low speed also happens. I thought the reason was because the truck has this stupid design that runs in 4 cyl. at times (they claimed its to save fuel which really does not, I compared the fuel consumption with my f350 2006, and the mileage is about the same - 15 miles per gallons vs 16 miles per gallons respectively) then shifting gears actuates the "full 8 cylinders" to "feel the power" of the 8 cyl. engine.

The transmission should be affected whatsoever if was designed properly regardless of the stupid idiotic engine "feature"(I got charged extra to have this stupid engine design - according to them - I realized after the purchase about this truck stupid "feature").

My solution was to get ahead in the loan relating to payments due and then, I sold the truck back to a Toyota dealer for cash, at that time truck only had 15,000 miles on it.