I had a similar issue like this before. I thought the TPMS sensors were defective. It turned out to be a a nail stuck deep in the groove of the tire. Perhaps try looking for nails in the tires?
I'm surprised you never lost any tire pressure over a year... I lose 1-2 psi every month or two. I always check every month or so.
2012 Mustang 3.7L V6 Premium MT
Airaid CAI/ Bassani Axleback/ BAMA 87 Performance Tune