The 3.6L engine in the applicable model years is subject to timing chain stretch and crankshaft Reluctor ring movement causing trouble codes, engine surging and possibly an engine no start condition. A wide variety of trouble codes may set to include P0008, P009, P016, P017, P018, or P019. The timing chains and Reluctor wheel should be inspected whenever servicing these vehicles. In an initial service bulletin release by GM it was recommended to replace the crankshaft when the Reluctor wheel moved but GM has since released a replacement Reluctor wheel which would require specialized tools to replace.
The included photographs from GM service bulletin PIP3423 detail the problem visually, but the solution does become very in depth. The engine should be removed to ease the service of these engines. If the timing chains have slack beyond the specification it is recommended to replace all components associated with the timing chains.
Poor oil change intervals can be an associated cause of these problems and it is possible other damage may have occurred within the motor. Engine replacement may be the safest solution to these vehicles. A motor oil analysis could detail the amount of steel particles in the engines lubrication system to aid in the correct method of repair.