battery charging light comes on when accelerating on an onramp and uphill

Whenever going uphill or accelerating onto an onramp, I will get the battery light and/or at least a "ding". I have replaced the battery, alternator, tensioner and belt in that order. A friend of mine is a service manager for a Chevrolet store and he has no idea what is causing it. Recently the light stayed on long enough that it created low voltage, which in turn caused several engine codes that have not come back since the reset. Any ideas?