Reduced Engine Power message?

My wife's 03 Tahoe has been giving us a fit lately. It has stranded her at the grocery store once and and one of her friends house as well.

It first started out acting like a dead battery. I found a loose negative battery terminal connection and it started up just fine. Then the next day it was a dead battery. I jump started it and checked the voltage from the alternator and it was putting out 14v. There was some intermitant times where it would go extremely low but would bounce back to 14v. This dont seem like an alternator problem to me but could be. The AC Delco battery still has the green glow in the indicator window so I dont think it is a bad battery.

When I disconnected the charger from the battery and let it iddle for about 15 minutes the Reduced Engine Power message came up and now the check engine light is on too.

Anyone know what this could be and how to get it cleared. With the REP message I cannot drive it anywhere.

Sorry for such a long post for my first post.

Joe I'm not real sure about your problem, but there is a module box mounted on your firewall. It is right in front of the driver side. This box has two plug-ins on the bottom of the box. Facing the truck,the plug on the left will give you both of those messages if it has been unplugged.Check to see if it is plugged in good. Hope it is as simple as this.If this is the problem it might take the check engine light a couple of times cranking it up and shutting it off before it goes away. The REP. message should go away as soon as it is plugged back in. Hope this helps.