2006 chevy colorado reduced power

Hi, I have a 2006 Chevy Colorado with 20,000 miles on it. On the way home yesterday, the alarm started to chime and the error message "REDUCED POWER" was displayed above the odometer. I also noticed a considerable drop in power and the CHECK ENGINE LIGHT came on and stayed on. I drove it the 1/2 mile home and then reset the odometer to clear the error message, but the check engine light still stayed on.

This morning, I called the chevy dealer who told me to bring in the truck. When I started it up, the engine rattled  a little and the check engine light went off and stayed off all the way to the dealer. It also had full power. The service tech put it on a machine and checked it, but found no issues. He cleared the computer and told me if it happens again to bring it back. He also said that the electronic throttle housing could be the culprit since it's due to be cleaned at 2 years or 30,000 miles at $119.00. Some how I don't think that is the issue. I drove it home without incident.

It worries me because my warranty will expire in June.