timing chain jump?
 

as you can see from what I went through in 2010, the chain can jump a tooth.

Removing the timing chain from your GM 3.1 V6 engine is fairly simple, once you get access to it. The timing chain is behind the timing cover and you must remove several components such as the water pump in order to access the timing chain, but once those are removed, the timing chain can easily be pulled off of the GM engine. You may need a puller.