I used to use a computer based program to track the mileage, but back in April of 2009 I discovered www.fuelly.com. I just sign in, input the odometer reading, gallons of fuel purchased and the price per gallon and Fuelly does all the calculations, plus you can customize it to show lots of different statistics. They even have a mobile app so you don't have to wait until you have internet to add your fuel-ups.
I had filled up the tank on the truck a couple days ago, and since I don't have a smartphone I went online to add it. I happened to click on the All Time Cost Analysis and this is the shocking chart that came up.
I really love my Tundra, and it actually gets good mileage for a 10 year old truck with 175,000 miles on it. If I'm not hauling I get right around 18 miles per gallon, and have had several tanks over 23 mpg. It's the hauling that kills me, the mileage can drop as low as 9 or 10 mpg if I've got a heavy load and/or large trailer. The lifetime average since I bought the truck in July of 2008 is 14.9 mpg, and I've been towing or hauling over half the time. That's still better than the 4-6 mpg I got with the Class C with no toad.
When it comes time to buy a new truck I'll do a ton of research, cost of ownership, number of repairs, etc. I'll also check on Fuelly to see what kind of fuel economy different makes and models get in real life. We all know the estimated mileage stickers on the window are not accurate unless you're a professional driver going 45 on a closed track with no accessories running and a good tailwind. LOL In a perfect world the rebuilt Caboose weight will come in low enough that I can continue to use my current Tundra, but I'm afraid it may end up too heavy.