I just got my 2006 silvarado K1500 and want to know if it is good to run in auto 4 wheel drive and does it kill my mileage

 

it will affect your mileage some, i would just keep it in 2hi until you need 4hi.

 

well, i guess you are as much Kramer as i am.
yes, it will lower your mpg.
and why do you want to do it anyway?
and yes, i do it once in a while. matter of fact, i even run her in 4HI for short runs. reason? well, me stupid believes that transfer case and front diff fluid is just sort of puddling down there in the casing. so, i stirr it time to time to get it up on the gears and chain. just for maintenance. and to make sure it runs. you don't use it - you lose it.
but no, don't run on it contionuously. ain't no AWD car, you know.

 

You will feel everything engage when you put it in Auto, almost as if you put it in 4 hi anyway.

There is no reason to if the pavement is dry. Two days ago, the roads were a combination of wet, snowy, icy and dry. I was concerned about leaving it in 4 hi for 15 miles of highway, so I put it in auto.

I never leave it there, as it will kill mileage