For me, the #1 cause of tough pork is over-cooking the meat. If you're of a certain age, then you can remember the Feds drilling into us that pork needs to be cooked thoroughly to avoid Trichinosis. That really hasn't been an issue for many decades. Cook the pork to about 140; you want a slight hint of rosy color. Also, consider brining your pork; it will add moisture to the meat. If you want to experiment with some flavor, perhaps creating a quick marinade of fresh papaya (a natural tenderizer, pineapple, garlic, thyme, rosemary, dried chili peppers (for a little heat to counter the fruit)lemon zest and olive oil. I would only let the pork marinate in this for a few hours as the pineapple and papaya will do its work quickly. I grill pork around 425; alternating between direct and indirect depending on the cut of meat and desired results.