It is possible you have one bad tire..it happens even with the better brands. try rotating your spare (or a friends wheel from another nissan) into each position one at a time to find the offending donut. Then you will not have to have a long conversation with the tire store. they will try to balkance that one wheel, and when they fail, get you a new one.
With one particular low end pirelli, I had a lot of problems with the bead spinning on the rim when you got it below 15 psi. This is not something I had ever experienced with bfg or goodyear though.