Gauges Not going to zero.

[3Hummer]

So it's my first couple days with my new truck and one thing I've noticed is that when I shut the car off the tach and speedometer go to zero, then slowly work there way back up to about 700rpm on the tach (which is where my truck idles at) and 5mph on the speedometer. Then when I get in the vehicle to start it up as I turn the key and the power is supplied the gauges return to zero until the engine starts up.

Is this normal? What could cause this? Is this a cause for concern? It appears the tach is reading just fine when it's running. And is 700rpm the typical idle point?

Thank you!