That thing is worth like $3000 here. They can get around 20 mpg if they are running right. I wouldn't drive one unless I had a backup car. They aren't very reliable and very slow compared to a 7.3 idi ford or a 12v cummins.the diesel models Get better MPGs than our gas motors my uncle had a suburban with a diesel and it got around 23 MPGs highway don't remember what he did in the city , Diesels are good on gas as long as you stay out of the throttle at idle they can run off about a cup of fuel for an hour try that with a gas motor ,
Also for 4500 that is CHEAP for what it is a common 4 door with no specials will run you that much
I think it is foolish to buy it for gas mileage, but whatever.
Time is money. It takes a lot of time to make bio. If the OP wanted to run bio, I would recommend an older benz with the 3.0 diesel. You can run bio, wmo, and atf mixed with diesel in those things and they are much better on gas and more reliable than a chevy 6.5Dont listen to hom get it and go bio diesel. Cheap and alot of mpgs. Dont even think abot it just go and make sure its good and get it