To know actual tow-ratings of any particular truck, the rear-end ratio must be known.
As for mileage, you can find amazing low mileage rigs if you keep looking. My current truck was sold brand new in Jan 2008. Over the next three years the owner put 600 miles on the truck. We figured it was sold to "an old man" that got too ill to drive and it took that long for him (or his estate) to sell it.
It was then resold in Jan 2011 to someone that put 6000 miles on the truck in 5 months. He was using it as a daily commute vehicle the the poor-gas mileage was killing him.
I bought it in July of 2011 with 6500 miles on it.