This one can vary quite a bit. But I’ll give you a very rough approximate figure…The truck itself will hold ~300 gallons. The tank he is hauling will hold ~9,000 gallons. So he’s got 9,300 gallons of fuel to work with.His mileage can vary quite a bit depending on the the model of truck, speed he’s going, and whether we want to presume his mileage gets better as his weight goes down. A truck made over the past decade or so can get anywhere from about 6mpg to about 10mpg — so that can change the results quite a bit.Let’s split the difference and say 8mpg.With 9,300 gallons and 8 miles to the gallon, he can go 74,400 miles before needing to refuel.Given the range of fuel economy we can see depending on the aforementioned factors, anywhere from 60,000 to perhaps as high as 90,000 miles could conceivably be possible.