2016 Infiniti QX70 Power Steering Problem

[Tom M]

I purchased a QX70 in Sept 2106. I now have 28,000KM on it. I have had a few problems. Cold weather (-40C) revs were once limited to 1500RPM until after 45 minutes of idling. Sometimes there is a lag in acceleration after flooring the gas pedal. Don't like that if I need to make a quick left turn. Now the power steering has failed (very stiff to turn steering wheel at slow speed, was Ok before today). No leaks, fluid level Ok and no noises from power steering pump and serpentine belt OK. Hmmm? I need some advise on what could be wrong with the power steering.