Truman - From Old English, literally "True Man," meaning faithful or honest.
Borden - Also from Old English, meaning "From the Boar's Den," which sounds a little ferocious, but the name doesn't bring up that image as much these days as much as that of a cow and/or brand of dairy products. What is really more relevant is that it is a fourth-generation name. Truman's great-granddad was Oscar Borden, his grandfather is Davis Borden, and his father is Benjamin Borden.
We like the name because it's uncommon, easily pronouncable, somewhat distinguished, and pretty much nickname-proof. And it just seems to fit him. Lots of people say that it's a big name for such a little boy, but we expect that he'll be growing into it soon.