The best way to answer this question would be to get it on a rack have it inspected and get a 4 wheel alignment.
I will say I've seen even new vehicles that look like their going down the road with a slight twist but they never exhibit odd handling characteristics or excessive tire wear.
Some things you can look at are:
Tire wear, any odd patterns on the tires?
Handling, will it drive straight if you let the wheel go at speed?
Does it grab grooves easily?
Does it wander when driving?
Any odd characteristics when turning?
Does it return to center after a turn?
Is the steering wheel centered?
On a level pad you can take measurements from point to point and compare them from side to side to ensure the trucks squared up underneath.
You can shoot a diagonal measurement from front to back on both sides to check for frame square.

 

The best way to answer this question would be to get it on a rack have it inspected and get a 4 wheel alignment.
I will say I've seen even new vehicles that look like their going down the road with a slight twist but they never exhibit odd handling characteristics or excessive tire wear.
Some things you can look at are:
Tire wear, any odd patterns on the tires? Rear right was worn more than the left, but I figured this was because I make sharper turns going right, than left.
Handling, will it drive straight if you let the wheel go at speed? Yes
Does it grab grooves easily? Not sure if I understsand the question, like grooves on the freeway? I guess so... :-/
Does it wander when driving? No. My old car had a bent rear crossmember for awhile (tree was in the way one day) and I remember that feeling, it would take off around corners. I don't get that feeling here
Any odd characteristics when turning? No
Does it return to center after a turn? Yes
Is the steering wheel centered? Yes
On a level pad you can take measurements from point to point and compare them from side to side to ensure the trucks squared up underneath.
You can shoot a diagonal measurement from front to back on both sides to check for frame square.

I'll do the diagonal dimensions tonight.

 

just measure from a fixed point and have a 4 wheel laser alignment done at a reputable shop. as far as the right rear tire being more warn thats probably because the right rear is the "power axle". look at it straight from the rear or even have your gf drive the truck and you can fallow her and see f you can notice anything. let us know how everything works out.