We have a Nissan UD with a 11.67lt motor. We have an 11 ton sticker (which is the weight of the bus as well) and tow a Kia Sportage - 1,700kg - and get 3-4 km to the litre, depending on what sort of hills we are climbing, or not.
1999 Isuzu NPR250A with 4HG1 engine, 4.6 litre direct injection. Automatic gearbox with electric overdrive, lockup on two top gears. 4600kg all up weight. 170,000 km on clock. Like to keep it around 2000- 2500 rpm to keep the noise down in the cab while maintaining good torque.
At 80-85 km/h it does a fairly reliable 15.6 litres/100km almost anywhere, but if we're in a bit of a hurry or there are a lot of hills it has been known to get up to 16.8 litres/100km.
As long as it just keeps going without needing repairs or any special attention we aren't too fussed that it's not the fastest or most economical van around. Diesel is relatively cheap compared to mechanical repairs!