Reduce Engine Power Light came on

I have a 2001 Chevy Suburban, the Service Engine Soon light came on as well as a notice in the status box, of Reduce Engine Power. The truck now just limps along about 20mph, It has 70k miles on it.

Any idea as far what is wrong or steps to go about finding out.

If the Service Engine Soon light is on, there will be one or more codes stored in the PCM. Autozone will scan for free.

//2000CAYukon