Check engine light

I am receiving an error message on my display which reads "Engine Power is Reduced". At the same time the message appears, the cruise control drops out, and will not re-engage. I also notice some minor surging while driving while this message is present.
If I turn off the engine and wait as little as 20 minutes, the message resets, the cruise will operate again, and the car behaves properly.
A secnd error message occasionnally appears which reads "Tighten Gas Cap". I have replaced the cap, but the message still occassionnally appears. I know that this is related to a pressure sensor in the tank, and that will be replaced.
Could the second message be triggering the first, or is the first message (Engine power) a totally differsnt problem, and if so what could it be?