2004 suburban has reduce engine speed what does that mean what could be wrong

SOURCE: What does reduced engine power light mean

this model has what they call fly by wire.. no accelerator cable. If the computer detects a problem in the thottle system it will not allow the engine to accelerate and will show reduced power and possibly set a check engine light. The dealer usually wants to replace the throttle assembly which is very expensive and usually un nessesary.
I have had a lot of succes with just cleaning the throttle plates real good.

SOURCE: 2004 chevrolet suburban service engine light

If you have - or can borrow an OBD tester - down load the diagnostic codes and check in the manual for their meaning. You can also shunt the dianostic port with a wire and read the flashes off of the instrument panel to see the codes being flashed and find their meaning in the appropriate service manual (this manual will also tell you how to properly shunt the dia port). A GM dealer will sometimes advise on this.

SOURCE: Reduced engine power came on i'n my 00 chevy

Ok I would start by checking your shifter to make sure it adjusted right and you can do this by looking at your shift indicator if that is ok then might have a bad manual shift valve thats in the transmission, if that valve goes bad it would tell the pcm that your transmission is being shifted into another gear while your driving causing the Power control module (PCM) to out you vehicle into reduced engine mode

SOURCE: I have a 2002 Chevy suburban and the reduced

Its telling you your vehicle has been placed in limp mode to prevent damage. You need to have your computer checked for codes that should lead to the issue causing the limp mode or reduced power mode