I recently took a phone call from my Dad regarding his latest vehicle purchase. My Dad has always been a loyal Cadillac owner and I was a bit surprised when he told me he had just purchased a low mileage 2013 GMC Yukon Denali with a 6.2L (L94) Vortec. He was very pleased with the vehicle as it had the same comforts and style he has always been accustomed to with his Cadillac. He was calling out of concern for something he had noticed after an oil change. I immediately got a sinking feeling and asked what’s going on? 
I’ll explain my sinking feeling.
Over the last 18 years I’ve worked within the aftermarket researching and developing engine components for domestic and foreign engine applications. When GM introduced “Active Fuel Management” (AFM) into their lineup of passenger cars and trucks, I became aware of the potential problems through research that could occur within the engines equipped with AFM and the many updates to components and procedures available to alleviate the very condition my Dad was experiencing.
For those of you who do not know what “Active Fuel Management” (AFM) is, it is a trademarked name for the automobile variable displacement or “Displacement On Demand” technology from General Motors. It allows a V6 or V8 engine to “turn off” half of the cylinders under light-load conditions to improve fuel economy.
So back to the call.
My Dad asked what should the oil pressure reading be on this engine? My response was 25 PSI, and I knew he was going there. Unfortunately he was only observing around 20 PSI after the oil change and anything less than 21 PSI can be an issue for the AFM set up. From his VIN, I immediately confirmed it was an AFM engine version and I advised him to be very careful of this condition as it may lead to an AFM lifter collapsing/sticking and causing a misfire if he did not diagnose the cause for the low oil pressure and repair the problem.
The following day in the process of driving the vehicle it developed a misfire. Too late !! I immediately recommended he take it to the dealership or a service center with the technology to correctly determine the cause of the misfire and has experience with this condition. Check here for bulletin. It is important to note the correct version of the AFM lifter to have installed as there are many versions available however not all may be current. The latest generation of this lifter at the time of this post is Genuine GM OEM # 12645725. 
There are known aftermarket suppliers that do offer the latest version as well.
There are also AFM Disablers available. It is recommended to check with an authorized repair facility to see if this is something you want to do and that it is properly installed.
Remember…..be aware of the signs before this happens to you ! It can save you $$$ and headaches !