When I start my truck I notice the volt gauge is down maybe around 10-11. So I let it sit and idle and then after about 10-15 sec or so it then comes up and sits right above 14. Is this common? Why does it do that.

03 Duramax Crew Cab LT short box (stock)

Thanks for the input

Packer

It is common. A search of the forums will show how common and explain why it happens in detail.

It has glow plugs and an intake heater that stay on for a while after it starts. They draw big time current and the alternator can't run them and charge the battery until they turn off.