Driving my Grandpa's 2011 I noticed the voltage gauge stays low like 10-11 low. Truck has like 5k miles on it, drove it up to 80 mph for ~5 hours combined and voltage stayed the same. Truck starts back up fine if you cut it off, is it normal for the voltage to be that low on the NNBS trucks? It has a 5.3 if it matters.