Having worked on the GM 3.6L
Having worked on the GM 3.6L V6, in a Cadillac ATS, I can tell you first hand about the timing chains, tensioners, and guides. First off, the labor to change them is 19.2 hrs! There's three chains and tensioners, two double geared sprockets, and a handful of nylon guides. I was able to acquire the timing set for about a third of dealer price from the parts store near me, and start to finish labor was 10 hours. All that from one bad tensioner!