Hi Tom,
Your 2011 has the LLT V6, GM's first release of a V6 version of the 3.6L engine. Your not throwing any codes is a bit puzzling, but here are the most common causes:
Low engine oil!!!! Check weekly on the dipstick as there is NO low oil warning light on these!!!! Most of these engines use oil due to poor ring seating when new and carbon/varnish buildup in the ring lands cause rings to stick and not seal properly.
Timing chain stretch/wear. GM specified the cheap syn blend oils in these until recently, and all GDI engine experience many times the fuel dilution and abrasive particulate matter shed from intake valve deposits mixing with the engine oil resulting in premature wear issues. But this is almost always indicated with CEL's on cam position vs crankshaft, etc. This can occur in as little as 30k miles, and some get over 100k miles.
Intake valve coking. This requires removing the intake manifold and cleaning the backsides manually. If you search here there are a couple great threads on doing this. Caution! do NOT use a engine running solvent based cleaning on these!!! The damage to the pistons and cylinder walls from loosening the hard crystalline deposits is not good. Those are safe on older port injection engines, but NOT today's GDI engines. This first shows up as soon as 20-30k miles if full synthetic oil is not used, and do not run the super thin viscosity oils. ONLY a full synthetic and Amsoil 5w50 is out favorite but any good 5w40 or better will give the protection needed. Our E2-X catchcan system prevents up to 85% of this and also keeps the engine oil cleaner far longer as this oil analysis shows:
And this is also important:
On the passenger side valve cover at the rear of it is a hard plastic line that connects to the top center of the intake manifold. There is a tab to push and it will disconnect from the PCV fixed orifice barb. This needs to be modified to the size of the 2013 and up design. Grasp the base with a pliers and twist while pulling straight up. You will most likely see it totally clogged. Drill the bottom 2 holes to 5/64" and the top one hole to 1/8". Clean and re seat back into the valve cover.
And as always, reach out to our Engineering and Technical support team of Engineers for any questions on GDI engines and more:
Tech@EliteEngineeringUSA.com