Despite the snow, hail, wind and blustery spring we are having I have managed to grill a few times. One of my favorites to grill is whole pork tenderloin. Generally I can't afford tenderloin, so I only buy it at Costco. Sometimes they come flavored (teriyaki, garlic, peppercorn) and sometimes they don't. The last time I picked up a package it was not flavored.
To a large ziploc bag I added a little olive oil, and lots of garlic and pepper, then added my whole tenderloin and marinated for a couple of hours. I like to get my grill nice and hot and sear the outside of the loin. Then turn down the grill, cover it and let it cook. I bought a great thermometer that works perfectly for the barbecue. I cook until the internal temp is about 155 degrees. Remove from grill, cover it with foil and let it sit for about 5 minutes. (Or until you can't wait any longer) Slice and serve. It is really good and super lean.
Everything you read says cook pork to 160 degrees. The extra sitting time before slicing allows for the meat to continue to cook. If this is a concern to you just cook it until it is 160, then remove from heat.
I know lots of people slice their pork tenderloin first, then grill. If you do this, please try it this way. The meat stays so moist and you'll never have dried out pork medallions again.