the PO2 here in Canada is bad for shearing the pin in the Actuater under the battery on the steering assist rod- pull it out & check the conection from the box if the pin breaks the command for power steering is cancelled & you are fighting everything so consequently no steering.

There should also be a fault code on the digital dash. if you can report it i can look it up.

there is a drive motor and gear box under floor board if steering is completly locked and not hard to steer and there are no codes then the steering shaft has a recycaling ball shaft that is most likley bad also check motor brushes and replace boot if cracked hope this helps

I have seen this happen on a cat before, are the drag link rod ends worn? The front rod end was worn and it would catch on the chassis cross piece. Does this thing have a power assisted drag link cylinder? If so check the ball rod in the valve on the cylinder itself. If not check the spindle stops just behind the steer tires and adjust them out and try it.

presume all is ok, axle itself looks fine, nothing loose! truck has been fine for over two years but now the drag arm from box has started to catch on chassis (appears to have bent but we have nothing to compare it with).

Are your spindle stops adjusted correctly? If you over extend the spindles they may be locking everything in place.