Question- why do you need a 600 mile fuel range?
Not about need, but I think it's fair to expect about 250-300 miles on the stock gas tank. I often drive to visit my Mom, she's about 350 miles. I have a '98 Tacoma 4cyl, it has about a 250-275 range, I've run out of gas once and almost a 2nd time a few months back.
I also have a piece of property about 175 miles away, so that's a 350 round trip. I can stop and get gas, that's not a huge deal but it's just having the range and with a 2nd tank you know you can flip the switch and you have more gas, even if you don't need to fill up, you have the gas to get you home. That's kind of how I look at it. I want this truck to be running well enough that I have the confidence to jump in it and drive for 400 miles if I need to. The extra gas won't help that confidence too much, but it adds to it. Between San Luis Obispo and king city there's about 35 minutes of no gas stations...that's where I almost ran out of gas a few months back.
The biggest driving factor for me is that I have 2 gas tanks in the truck, but the original is not being used. It looks in pretty good shape, under the seat, but I haven't even inspected it closely yet. I already bought the fuel pumps and toggle switch, so worst case I've wasted $30.
EDIT: OTOH, I haven't needed more than 10 miles range in the past year, and that would be generous! Luckily I haven't needed to depend on the truck for transportation.
