The pulling power behind your motor is provided by the GMC Piston when it is in action. This cylinder shaped engine component is designed to withstand thousands of explosions per minute and still remain intact in the interior of your GMC truck engine.
To seal the edges of the piston in the combustion chamber are a set of piston rings. These are in place to fill the minute level of clearance between the cylinder walls and the piston. When there is a problem with compression, it is generally the rings and not the piston that is faulty and in need of being replaced on your GMC truck.
The most common way a GMC piston is damaged is when either a metal object is accidently dropped into the spark plug hole during a tune-up or the wrong heat range of a spark plug is used in a tune-up. It is also possible for the valve to penetrate the piston if the timing chain or belt is off by just one tooth and they make contact.
The problem with placing a spark plug with a greater heat range than what is recommend is that the extra heat it generates is too much for the top of the piston to handle. In the short term the GMC engine will perform slightly better, but the additional heat on each explosion when the engine is running will produce a hole in the top of the piston. Once this hole is all the way through the top of the piston, that cylinder will have zero compression and be considered a dead cylinder. Only the replacement of the piston will remedy this condition in your engine.