W900l cat c15 mpg?

I'm looking to buy a 07 w900l day cab with cat c15 accert twin turbo, hp raised from 475 to 550, 18 spd 4:30 rears.
Now i kno it all depends on what I haul and how heavy is my foot, I haul containers half the time I'm empty and the other Half loaded. Loads vary from 15000lbs-52000lbs gross without tractor. I drive around 400 miles a day half empty half loaded 99% highway at 65mph. Im curious to know what mpg I should expect from this truck? I get around 6.5mpg on my international with a m11 350hp 10spd

 

Yea that's what I was thinking too but I can't find any kw900l with a lower ratio

 

Dirty low walker yes it's a over drive

pagejam6nz I was thinking about swapping the rears but wouldn't 2.64 be too low? And yes I hope Mr Haney would give his opinion. Or does anybody know how to contact him?

 

Bubbanbrenda thanks for the links one of them is too far away for me the other it's the older interior I wanted the new vit interior. And the white one looks good I'll give them a call tomorrow.

 

Cool thanks for sharing. By any chance you guys know where mr Haney's shop is located?