[72 k15]

I have the 8.1l It gets bad millage but thats expected, now the 8.1 vs the 6.0 I would go for the 8.1 the 6.0 only get 1-2mpg better max anyway and you will have way better towing power. I actually have a 8.1 and zf6 6 speed Manuel trans. Driven the 6.0 and the 8.1 and like the 8.1 better downshifts less when towing runs less rpm ect.... If you are worried about gas mileage I would just get the diesel. I got the 8.1 due to maintenance cost being lower and im willing to pay more at the pump to keep the maintenance cost down. Now dont think the 6.0 is a bad motor because it is a great motor but if you are towing a lot the 8.1 will outclass it. If you have any questions ask away.