Gas mileage with long box

I'm getting ready to sell my 02 2500 duramax and I'm looking at 2nd gen Tundras. Just looked at a long box 2012 and was wondering how much the extra truck affected mileage. I know it wouldn't be much but I'm just trying to balance the extra length with the tundra being a work truck and a family trip truck as well. Don't need the extra length with family use but might be handy for work occasionally. Not sure if having to deal with the extra length will be worth it. Also, I'll have to drive in a city maybe once a week and occasionally my wife will use it.

 

It depends how you drive. I use mine as a work truck and get better mpg than the 4.7.

 

18, that's encouraging. And that's with the 4.30 rear end?