Jerry,
The Jake brake that you have is a great system that is pretty much trouble free. It is far superior to the exhaust brake which does raise pressures by restricting the flow of exhaust.
The Jake system basically stops the fuel flow and when the cylinder goes into a compression stroke there is no combustion so you now have a compressor using energy to compress the air in the cylinder. This is a normal compression stroke so the engine never sees any increased pressure or excess stresses. If that air was not exhausted at the top of the stroke then it would drive the cylinder back down so a small third valve is incorporated which opens and the air is exhausted at the top of the stroke which is the distinct sound that an that an unmuffled Jake brake puts out. Your rocker switch drives the mechanicals to utilize all 6 cylinders or just 3 which is the Hi/Low option or off.
Jerry, this is a great system that just needs a little attention to select the right gear while using it if the preselect is not right for the hill at hand. It is all pretty much bullet proof and one of the joys of having a C12.....the other is the power :-)
Later Ed