It's a common term where used autobody vehicles. In which case it's where longitudinal rails tie in cross bracing forming a boxed section. I've never heard the term torque box used in the description of a full frame.
Typically these frames will tweak in this area. This shortens up the rail on one side and instead of measuring square the measurements graph out as a diamond. It can be a very shallow dip in the frame rail and be hardly noticeable until you start measuring.
Are these measurements something that I could do myself or would it require a frame shop with the lasers and fancy tools?
What these guys said about the steering.. but also let's not overlook 270K miles. Many steering gearboxes (and the front end in general) are worn out at that point. Even so, sounds like you made out pretty good for the money!
Richard
This comment brings me to today, because I have a little bit of optimistic hope on that. It's pouring today so I can't get out to look under it. But I did take it to the DMV to get tags and I was experimenting with a thought on the way:
If I get the steering perfect on a very flat road, the truck WILL track straight until I hit a bump or the road banks. I'm not exaggerating when I say there's 45 degrees of slack in the steering, so it's hard to do, but i imagine if the frame was tweaked, it would pull one direction constantly, right? It doesn't seem to prefer one direction over the other.
Some other stuff that may or may not be important:
-the slack in the wheel isn't center. Steering engages left and right at roughly 0 degrees and 45 degrees, respectively. Not sure if that's a good, bad, or irrelevant sign.
-I can't see any noticeable difference between any of the tires as far as wear goes, although I've only put 200 miles on the truck so far.
-I guarantee that steering box has gone the full 270k. Which is kinda surprising considering how much I've seen under the hood that's new.
Biggest question is, if you didn't want to read all of the blabbering in this comment, how do I get a definitive answer without just throwing parts at it and seeing if it gets better?