I'm looking at upgrading from my s10 to a diesel. I want a full sized pickup that's good on gas, and seeing that diesel is cheaper than gasoline right now it seems like a good choice.

Here's the one I was looking at...

2004 Chevrolet Silverado 2500HD LT Pickup Truck - Calgary Cars For Sale - Kijiji Calgary Canada.

Is this truck over priced for its KM's?
How many Kilometers/Miles to a tank and how much to fill?
Are these engines reliable? Long life span?
Are the Allison transmissions good? again, lifespan?
What are common problems with these trucks?

I have a 2009 GMC Sierra 2500HD with the Duramax diesel and Allison tranny but it was my dads. He is no longer with us and it is not my truck so I don't have the chance to ride the truck dry and see what it gets for fuel economy. If I were to buy the truck in the Kijiji ad, I would straight pipe it and eventually chip it which I would hope would add fuel economy.

Thanks guys.

Remember the ad is in KM's, not miles.