I have a 2000 dak with the stated problem, the only replaced steering component was a steering rack about 5 years ago. It was recently aligned after changing rims going from a 15 to a 16

 

return to center occurs from positive castor angle. when you turn the spindle is angled due to the castor....this lifts the fender....gravity forces the weight of the car down and forces the spindles to sit at their lowest point.. this returns the wheel to center. post the alignment printout and verify the castor is correct.
there are other factors but rule out caster first.

 

Exactly when did the problem occur and what happened right before it manifested? The one time I experienced this, I had replaced my ball joints and a few other components. Well, I had over torqued things and the steering would not return on its own. Had to go back in again and torque things to spec.

 

the truck has been in the family since it was bought brand new, been through a few generations and right before me my dad had crashed it in. It sat in my driveway for about 5 years, and started up instantly with a new battery after that it had the rims and tires changed then aligned, other than that the only changes have been a new bumper, hood, and lights

 

Check the lower intermediate steering shaft. The u-joints eventually will bind up. I had the same problem with my '00.

 

how can I tell if they're binding

 

The easiest way is to disconnect it - but then you may as well replace it.

Try soaking it in penetrating oil.