Ford f450 questions

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Hey guys,
i am considering upgrading to a ford f450 drw 6.0L diesel. can anyone tell me what to look for when buying it used? it has a dump bed. it is a 1997 model. around 67K miles. he is asking $8000, but i think i could talk him down atleast $1000

what kind of gas mileage does it get? from what i see diesel is a little more expensive per gallon, but might run longer.
any information on f450s would be appreciated.

at the moment i have a toyota tundra and is real limited when doing hauling of any kind, like leaves, debris, etc... its a great truck, but i will have to get a trailer or upgrade.
thank you very much