guage reads at 12 when driving, about 11.5 when idle, but it does show correct voltage when not running about 10-11 when off. but replace batter and alternator and still got the problem. what do you think?

 

double check the voltage with a digital multi-meter

 

Do not trust any readings from the factory gauges! They are very unreliable.

As Icemark said, check the voltage with a good meter. As long as you are not having drivability problems (no start, stalling, dimming lights...) you should be fine.

 

it should be reading 14 - 14.4 volts when running