Pork no longer has to be cooked well done because it no longer carries Trichinosis, which was why you used to have to cook it to shoe leather. It's been eradicated in commercial pork. One of the problems in that is that pork has gotten leaner, making it not as moist. If it is overcooked, it will definitely be tough. A good temp for pork is 160, with a 3 minute covered rest (for a chop, 10 minutes for a roast) after taking it off of the heat.
Watson