Do I need to treat the ends of PT lumber?
The pressure treating commonly used today does not penetrate the lumber 100%. I'm assuming mostly financial reasons at play here (time, cost of materials, etc). I highly suggest any cut ends that you see untreated wood at the center, be treated with off the shelf, brush on preservative. You will be well served here. Why take that chance over a few extra minutes, and a relatively small amount of dollars on a presumably several hundred, to several thousand dollar investment?