2001 F250 ZF6 6-speed standard, 3.73 rear end. Pulling about 7,000lbs get 11mpg towing at 70mph. I would love to try out the 8.1, as well as the ford v-10. If an 8.1 came up with a good price when I was looking a few months back, I wouldn't have hesitated getting one. From what I read, a bigger fuel tank would be one of the first things I would add. Old truck, new truck, they are all subject to break down, and they are all subject to expensive repairs. The newer ones are nicer, and more expensive, the older ones are simpler, and cheaper. Take your pick and enjoy it, if you don't enjoy it, sell it and get something different.
