What psi should i run on my bf goodrich all terrains?

I have a GMC sierra 1500 Z71 and dont really pull anything. I do go off road from time to time, and wanted to know what psi i should have it at. On the door it says 50psi, but that is for a smaller tire i believe. does it matter? i was told 35 by a "tire expert", but that just seems too low. I had it at 65 before and it felt like it was dragging just a tad.