that NUT you are referring to is the damper to take up the rack slop as it wears gradually. What you are suffering is from weak pressure to the rack valve body - because I doubt the valve body of your newish toyota would jam so soon unless someone put something else in the fluid too or your fluid is foaming up under load.
It can also be because of excessive lugging of the pump, there are somethings not to do in any power steering car (even mentioned in the manual)
do not spin the wheel very fast in a stationary car
do not hold the steering at full lock for more than 3 seconds
the last bit that maybe causing hard steering is that your IACV is not working properly and not regulating RPMS at idle speed under pump load - causing the pump to slow down and lose line pressure.
Note the idle speed of the engine and does it drop with steering load? And which fluid are you using for the power steering? type and brand please