Greetings and Welcome to Just answer.
In these vehicles, the Reduced Engine Power is the indication there is a problem with the throttle assembly. These engines use an electronic throttle assembly that is controlled by the engine computer and a sensor on the fuel pedal. What I suggest you do first is get your Trailblazer scanned for the code. A fault in the throttle to cause that will also have set the check engine light. IF the light is on now, then you can get it scanned at most any part store and they will do this for free. If the light has gone out, then the code is in history and you will need to get it scanned by more than just a code reader. You need to use a scan tool for this. A scan tool is very different than a code reader. Scan tools are larger, can scan and control certain systems of the whole vehicle, and usually cost about 2000+. A code reader will only read emission related codes and that limits them to reading the engine and transmission modules. Given the cost of the scan tools, it is usually cheaper to get a shop to read the codes. If they are honest, I would imagine that $20 is fair to stick the machine on and read codes.
If you reply back here with the codes I can tell you what they mean and direct you in a repair or further diagnosis.