The AFM (Active Fuel Management System) is a GM technology. This system allows half of the Engine’s Cylinders with freeway driving to improve the Fuel Economy. The system was designed to increase Fuel Economy but not reducing the performance of this large Engine. The V-8 Engines have the capability to tow and haul items, needing a powerful Engine to perform. With technology, it has the capability to switch off Cylinders when not going up a steep hill with a large load or needing more horsepower. The System is seamless in it’s ability to turn off or on these Cylinders. 
However, as customers between 2007-2013 have noticed the excessive oil consumption issue lies with a defect in the 5.3-liter V8 engine. Somehow the AFM allows the Oil to get past the Pistons, so it enters the Combustion Chamber. It then burns out or hardens and cakes (as shown in the picture) in the Cylinders. It is not something that is noticed, no blue smoke out the tailpipes, so Pistons and Cylinders can get damaged. With this Vehicle the Engine itself was damaged. 
In further reading, GM has:
By 2019, GM had developed Dynamic Fuel Management (DFM) also known as Dynamic Skip Fire, which is a smarter version of AFM. While AFM would shut-off the same cylinders every time the system would activate, with DFM, the engine has up to 17 different patterns it can run in depending on load and other inputs.
