I was driving my Wife's Denali and noticed that the Voltage Gauge was down to around 12-13 after we have been driving awhile down the road. Well it was going in anyway and the Dealer thought one of the legs in the Alt. might be dropping out. They put a new Alt. on it and it still does it. No lights come on and everything is fine but just odd. I do know some models do this for fuel economy but has anyone else see this?