Opinion on 1998 kw t800 n14 460 13 speed

Can you guys pls tell rough estimate
Overall clean nice truck per pics , engine overhauled 150k ago by dealer , new tranny , new Bridgestones all around ( supersingles) , new brakes . Owner send shot from computer of last trip 6.73mpg from 2500 miles .
Most likely will be getting rid of my stinger car hauler ( before I thought just trailer ) ...just speculating on diff trucks and options , I have 1999 kw 900 ...looking for something more MPG friendly

 

Really like t680 or 700 ...but I doubt I can find something with bad engine ( have spare ) very cheap

 

Im getting second truck ...w900 gonna stay , I'm getting rid of Pete 379 ...Pete mpg 4.8-5 being stinger car hauler . ..
I know it's mostly about driver and setup but I believe same driver will do better in more aerodynamic truck with mpg friendlier than brick design with tuned up cat ...don't get me wrong I love 379s and w900s but if I gain 1000$ a month on fuel savings - why not . I used to have Freightliner century 2005 with 12.7 and 10 speed , ecm , egr delete and pre egr turbo - that truck was pulling on the 10th speed on the cruise control whole i80 in PA and i76 back with 75k ....no I wasn't lagging the truck ...and it was doing close to 7mpg

 

Hate to get rid of Pete , I'm sure it will do over 6 easily if I remove head rack for cars but in carhauler world I believe it will be hard to sell just stinger type trailer ..not being a combo

 

Thanks but I don't wanna take my chances with emission equipment.

 

Binder yes , miles 1.5mln , pulling dryvan in dedicated route 2500 miles weekly ...I know super singles is emergency call when it's flat but I believe it save some mpg