READ FIRST:
GM has very common issues with their V8 engines. Mainly the 5.3L engines with AFM (active fuel management). The AFM lifters tend to fail, and stick or collapse. Keeping good oil, and plenty of it in the engine, is KEY. These engines also have a bad oil consumption issue, which GM say is "in their specs". ALL YOU NEED TO DO IS REMOVE A VALVE COVER ON SUSPECT MISFIRE CYLINDER, AND WATCH FOR NO MOVEMENT ON THOSE ROCKER ARMS. There is a TSB leading to the passenger side valve cover clogging up in the breather area, as well as piston rings on either cyl#7 or cyl#8 sticking. Make sure you check your oil and change it frequently.
In short, we changed the engine out due to this unit having a serious oil consumption problem and low compression due to another common issue of sticking piston rings on cylinder 8 or 7... ANOTHER class action lawsuit again on this platform.