The tank in all Hilux's from 2005 onwards is 75L, petrol or diesel. If you're getting 650km to a tank in a v6, then congratulations you've got a rare find there unless you're doing alot of highway kms. The majority of v6 owners average around 15L or so combined cycle and that gets worse off road. Diesels get around 10 to 10.5 and that goes upto around 12L off road. If you have a supercharged v6 it gets even worse on average. I don't know where the idea that diesels cost so much more to service came from, you don't even need to worry about plugs and leads - it's pretty much just oil and filter, plus the occasion fuel filter every 25,000km (about $20). The only expensive problem you will have is if the injectors go, and that's mostly occurs when putting cheap or contaminated diesel in it. Mine's an 05 model with the original injectors and I had them tested 2 months ago and they're still in spec. Both engines have their place - if you're a tradie or like going off road alot then the diesel is the best option by far when it comes to heavy loads or low speed torque.