The basis for cleaning the top end of your engine is pretty simple. The EGR system recirculates exhaust gases which deposit carbon all over your intake manifolds and the intake port on the heads. The backside of the intake valve is also a concern as the carbon not only attracts the fuel, but also changes/lowers your airflow. Efficiency and horsepower are lost over time.

To use the GM top end cleaner, you can use either the spray or the liquid, though I prefer the liquid.

First, start in a well ventilated area. This is going to cause quite a smoke show

Let the engine idle to warm up, or if already warm, let it sit for a minute or 2 at idle to heat up the entire engine. Then, using a smaller vacuum line, like the one going to the fuel pressure regulator, stock a vacuum line into the bottle of cleaner. You will need to hold the throttle open a little more so the engine doesn't die. You need almost all of the can to go through the engine. Before its completely gone, either close the throttle and hope the engine stops as well, or have someone else turn the key off. Reconnect the vacuum line to whatever you took it off of and let the engine sit for 10 minutes.

Starting the car/truck after 10 minutes is going to be difficult. It will probably turn over a bit before it ever catches, and then it will probably run a little rough. You need to rev it up a little and get it so it will idle. Then, after its ok for idle, you need to drive around to clean it all out. This will cause a lot of smoke still so hopefully you can do this somewhere without too much traffic. Varying the throttle and increasing the max % of throttle over time (say a couple minutes) will eventually get it all cleaned out and running better.

There are other methods to this so if you would like to add anything please leave a comment.