2001 Ram power steering problems

2001 ram with5.9 diesel. problem started on a very cold morning. couldn't turn the steering wheel and noticed hard brake pedal. put a tarp over the truck and used a salamander to warm it up. after a few hours, I tried it. brake pedal was good and the steering worked but felt like a loose belt.moved it in to my shed(unheated) a few days later i moved it outside and after a few hours the assist was gone again.the pump does not appear to be working but i can't tell what drives it, front is enclosed. didn't want to start ripping off covers without some idea of what i may be getting into. anyone else had this problem?