A few good updates...
After I picked up my truck from the driveshaft balancing shop, it was 90% better. On the highway, it you really listen, you can still hear a faint noise at the same conditions, but balancing the driveshaft has taken most of the noise and all of the vibration away. If you're not listening for it, you won't hear anything.

As far as the truck's past, I have no history for it. I picked it up from some no name crap dealership in Massachusetts, who said it was a trade in and had no info on it. From what it looks like, it may have been hit before, I see an aftermarket rear door and body work done... The truck's carfax report shows past registrations in Boston, and if you've driven there, you'd know that the roads are terrible. It definitely wasn't offroaded or screwed around with, way too nice of a shape...interior is spotless, less than normal wear on most else...

But what can I say? When you see a great truck, you give it a thorough inspection yourself (and from toyota too), offer a fair price, buy it, and take care of it. Most people (excluding readers of this site) don't understand the 'take care of it' part, but my truck's in good hands now. <img src="/forums/images/graemlins/cheers.gif" alt="" />
Next step: exhaust leak and new shocks...
Thanks for all input, I'm still checking everything suggested out