My 2012 Avalanche had dead batteries when I came back to the lake after a week away. The batteries were original, manufactured in 2011. I got it started with a booster, but the check engine light was on, and it seemed to be running rough. The dealership suggested that was just due to low voltage. I replaced the batteries today and put it back on the water. It started fine, but the check engine light remains on. It would go off when i got up to higher speeds and RPMs, but as soon as I pulled back on the throttle, it came on again and remained on. It would go off again when I hit high speeds and RPMs. Any ideas why? or how to get rid of the problem?